We must conjugate the verb mover in the preterite.

Given that Los indígenas acts as a third person, plural personal pronoun (ellos):

Los indígenas movieron estas piedras enormes sin usar animales./ The native people moved these huge stones without using animals.

Next, we are going to use the verb dudo (I doubt) in the subjunctive mood to express doubt.

Dudo que los indígenas hayan movido estas piedras enormes sin usar animales./ I doubt that the natives moved these huge stones without using animals.

movieron… Dudo que los indígenas hayan movido estas piedras enormes sin usar animales.

We must conjugate the dibujar mover in the preterite.

Given that Los indígenas acts as a third person, plural pronoun (ellos):

Los indígenas dibujaron naves espaciales.

Next, we are going to use the verb hacer (to make) in the subjunctive mood to express doubt. The expression “Es imposible” (It´s impossible) communicates doubt as well.

Es imposible que los indígenas hayan dibujado naves espaciales./ It is impossible that the natives have drawn spaceships.

dibujaron
Es imposible que los indígenas hayan dibujado naves espaciales.

We must conjugate the verb unir in the preterite.

Given that Ellos is a personal pronoun (3rd person form, singular):

Ellos unieron las piedras sin cemento./ They joined the stones without cement.

Next, we are going to use the expression “Es poco probable” (It´s not likely) to express doubt.

Es poco probable que ellos hayan unido las piedras sin cemento. / It is unlikely that they joined the stones without cement.

unieron
Es poco probable que ellos hayan unido las piedras sin cemento.

We must conjugate the verb medir in the preterite.

Given that “Los arqueólogos” acts as a third person form, plural personal pronoun (ellos):

Los arqueólogos midieron todas las piedras./ The archaeologists measured all the stones.

Next, we are going to use the expression “No es posible” (It´s not possible) to express doubt.

No es posible que los arqueólogos hayan medido todas las piedras./ It is not possible that the archaeologists have measured all the stones.

midieron
No es posible que los arqueólogos hayan medido todas las piedras

We must conjugate the verb descubrir in the preterite.

Given that Nosotros (us) is a personal pronoun (Yo form, plural):

¡Nosotros descubrimos el observatorio! / We discovered the observatory!

Next, we are going to use the expression “No es cierto” (It´s not true) and the subjunctive mood to express disbelief:

No es cierto que nosotros que nosotros hayamos descubierto el observatorio./ It is not true that we have discovered the observatory.

descubrimos
No es cierto que nosotros hayamos descubierto el observatorio.

We must conjugate the verb pesar in the preterite.

Given that Yo is a personal pronoun (1st person, singular:

Yo pesé toda la cerámica./ I weighed all the pottery.

Next, we are going to use the expression “No creo” (I don´t believe) and the subjunctive mood to express doubt, or disbelief:

No creo que yo haya pesado toda la cerámica./ I don’t think I have weighed all the pottery

pesé
No creo que yo haya pesado toda la cerámica.

We must conjugate the verb medir in the preterite.

Given that Ramón acts as a third person, singular pronoun (él):

Ramón midió correctamente la distancia entre estos dos monumentos. / Ramón correctly measured the distance between these two monuments.

Next, we are going to use the expression “Es dudoso” (It’s doubtful) along with the subjunctive mood to express doubt:

Es dudoso que Ramón haya medido correctamente la distancia entre estos dos monumentos. / It is doubtful that Ramón has correctly measured the distance between these two monuments.

midió
Es dudoso que Ramón haya medido correctamente la distancia entre estos dos monumentos

We must conjugate the verb comprender in the preterite.

Given that Nosotros is a personal pronoun (first person, plural)

Nosotros comprendimos la función de estos óvalos./ We understood the function of these ovals.

Next, we are going to use the expression “no es verdad” (It´s not true) along with the subjunctive mood to express disbelief.

No creo que nosotros no hayamos comprendido la función de estos óvalos./ I do not think that we have not understood the function of these ovals.

comprendimos