Question

Hay muchas nubes en el cielo. El pronóstico dice que ______________ llover.

vas a

va a

voy a

vamos a

Answer 1

There are many clouds in the sky. Said prognosis
ti going to be va a

Answer 2

la respuesta seria "va a" llover porque las demas te darian una oracion incorrecta que no se entenderia, ademas de que "voy" y "vamos" estariamos hablando de alguien no algo..
Espero haberte ayudado

The correct answer would be "va a" because the others would give you an incorrect sentence that wouldn't make sense. Besides "voy and "vamos" is talking about someone not something

Hope this helped