Write the correct form of the verbs in parentheses. 

1. I ____________ a career in design, but I _____________ to change to teaching. (choose; decide)

2. The exam ____________ when the fire alarm ___________. (just start; ring)

3. By the time the teacher ___________ , the students ___________ the classroom (arrive; already leave)

4. Linh ____________ as a construction worker for 10 years before he ___________ an architect. (work; become)