Question

Mientras tú ___________________ en la bibloteca, yo estaba leyendo el periódico en el parque.

A.
estabas
B.
estás
C.
estábamos
D.
estaban

Answer 1

The answer is estabas because you ar describing an ongoing action which makes it imperfect

Answer 2

For this case we have the following statement:

While you ___________________ in the library, I was reading the newspaper in the park.

What we should do is fill in the blank with the correct verb.

The correct verb conjugated in the past simple is:

You were

We have then:

While you were in the library, I was reading the newspaper in the park.

The translation of the sentence in English is:

Mientras tú estabas en la bibloteca, yo estaba leyendo el periódico en el parque.

Answer:

A. estabas