3. If / In case Carl arrives before I get back

4. Though / Although / Even though he is in his eighties

Part 3

I. 1. for 2. of 3. to 4. of 5. as

II.

1. There is a strong possibility that there is life on other planets.

2. The plan for building a shopping square in the city centre has gone through.

3. The tall and thin girl reminds me of my cousin Linda.

4. I gave Bill a watch on his birthday, but I expected nothing in return.