Answer:
The answer is A, Amino group.
Explanation:
This is an amino group because we can look for familiar patterns in molecules to identify  functional groups. An amino group looks like NH2, meaning that there is one nitrogen (N) and two Hydrogen (H2). We can see this in the picture. All four groups have fairly simple patterns to look for - I'd look up the pictures of them and take a look if you want to learn all 4!
