1) is wrong. It can be a line in the same direction with an included angle of 0.

2) Right

3) Wrong, as long as it is the other way around, it doesn't need to be equal in length. Left => Correct.

4) Yes, it's easy to understand. On the left is b+b, two * * line vectors, and on the right is (a+b)+b, not necessarily * * * lines.

Choose B.