PPReview1-3 10

mudfish

10. Stars provided early astronomer with a reference system for measuring the motions

      of planets, the Moon, and the Sun.

Answer: A

I agree that "astronomer" should be "astronomers", but I think there is another wrong that is D "the motions" should be "the motion".

According to the Longman Dictionary,

Motion: [UC] the process of moving or the way that someone or sth moves.

                   ex : the motion of the planets

             [C] a single movement of your hand or head, especially one made in order to   

                   communicate someone

                  ex: a motion of his hand

require

No, there has only one answer:a

the montions is right.

the + motion,motion

they are both ok, the point is the meaning of the sentence.