What does the + symbol mean in the following grep regular expression:

exams 101-500 V2 101-500 exam 0 Comments

What does the + symbol mean in the following grep regular expression:

grep ‘^d[aei]+d$’ /usr/share/dict/words
A . Match the preceding character set ([aei]) one or more times.
B. Match the preceding character set ([aei]) zero or more times.
C. Match the preceding character set ([aei]) zero or one times.
D. Match a literal + symbol.

Answer: A