Please help.

D - Velocity is speed with direction.

Explanation:

The difference between speed and velocity is simple:

Speed can be represented as the change in distance over time, while velocity is just speed with direction.  

For example, the speed of an object that traveled 10 meters over 5 seconds traveled at 2m/s.

But, if that object was traveling, say, North, then the velocity of the object would be 2m/s North.

On a side note, any change in the velocity is just acceleration, whether it is changing direction or slowing down.

Hope that was of help :)

1 - wave length

2 - amplitude

3 - crest

4 - trough

explanation:

duh.

root word, prefixes, and suffixes