Dot Product Rules Multiple choice

[Lothar]

Homework Statement

See the image
http://tinypic.com/r/33z6vz5/7

Homework Equations

The rules of dot product multiplication.

The Attempt at a Solution

I've determined that 2 of the solutions are valid, while two of the choices are invalid. I thought C and D looked correct, making A and B incorrect. Unfortunately it wasn't so. I'm down to my last submission and I really don't know what I'm doing wrong.

Thanks you

 

[vela]

Why do you think the answers are valid or invalid? You need reasons better than an answer "looked correct."

Hint: What type of quantity, vector or scalar, is the dot product of two vectors?