Question

While the dog.............in the backyard, it.......... a bone.

a. dug / had found
b. were digging / found
c. was digging / found
d. had dug / found
e. was digging / had been found​

Answer 1

While the dog was digging in the backyard, it found a bone.

c. was digging / found

Past Continuous, Past Simple (одно действие прерывает другое в его продолжении)