Which one of the following reasons helped make Mendel successful with his genetic experiments?

a) He had a strong background in mathematics.
b) He was very careful, kept track of all his data, and followed the scientific method closely while doing his research.
c) He kept very detailed records of his research.
d) He was basing his research off of research that had been done by other scientists before him.
e) All are reasons Mendel was successful with his genetic experiments.