When I was in primary school I was told that the earth around the sun.A. had travelledB.

问题补充：

When I was in primary school, I was told that the earth around the sun.

A. had travelled

B. would travel

C. travels

D. travelled

答案：

A. had travelled

B. would travel

(答案→)C. travels

D. travelled

解析：考查时态。客观真理的动词形式即使在过去也是用一般式,因为这个动作是一个客观的持续,过去或者现在或者将来都不会改变。所以用的是现在式，选C。