Question

My sister ... in Moscow for 6 years. has been living lives had been living

Answer 1

My sister has been living in Moscow for 6 years.

Answer 2

Based on the provided sentence fragments, the correct completion would be:

"My sister has been living in Moscow for 6 years."

The present perfect tense "has been living" is used to indicate an action that started in the past and is still continuing up to the present moment. In this case, it suggests that your sister started living in Moscow six years ago, and she is still living there now.