Step 1 - Understanding what "pentyl" and "ethyl" mean
Whenever you have some part of a molecule's name ending in -yl, it means this group is a ramification, or at least can be interpreted as such. Therefore, if the molecule is a cyclopentyl ethyl amine, we got to look for the molecule in which a cyclopentane and an ethane can be seen as ramifications.
Step 2 - Identifying the correct structure
Note that in molecule A, the N atom is part of the cycle. Therefore, it's not a cyclopenthane ramification. In molecule B, on the other hand, there is indeed a cyclopenthane as ramification.
Therefore, the correct structure is molecule B.