1.Helen (do) it by 10 o'clock yesterday. 2. She (translate) the article before the film (begin). 3. I (see) him yesterday.

1.Helen (do) it by 10 o\'clock yesterday. — Helen had done it by 10 o\'clock yesterday

1. She (translate) the article before the film (begin). — She had translated the article before the film began.
2. I (see) him yesterday. — I saw him yesterday.

4. I (see) him before the accident (happen).— I had seen him before the accident happened.