Choose the mistake in each sentence. Then correct it.

When I (A) was looking for some books (B) in the library, I (C) was finding an interesting biography (D) about General Vo Nguyen Giap.
1. was looking
2. in
3. was finding
4. about
(A) At the age of 16, Walt Disney (B) was dropping out of school because he (C) wanted to join (D) the army.
1. At
2. was dropping
3. wanted
4. the
Vo Thi Sau (A) was caught while she (B) tried (C) to attack some (D) French soldiers.
1. was caught
2. tried
3. to attack
4. French
(A) While the famous author (B) read from his biography, everyone (C) was listening and (D) taking notes.
1. While
2. read
3. was listening
4. taking