Question

She......in Switzerland for 10 years when she was a child
a. Had stayed
b. Have been staying
c. Stayed
d. Had been staying​

Answer 1

She had been staying in Switzerland for 10 years when she was a child.

Option (D) is correct.

Explanation:

This sentence is an example of past perfect continuous tense.

The formula fro sentence making is:

Subject + had been + 1st form of verb + ing + object

"Since" or "for" is also used in these sentences to indicate the particular time period.

Thus the sentence She......in Switzerland for 10 years when she was a child

can be written as;

She had been staying in Switzerland for 10 years when she was a child.