Which regular expression or command should smith use?

The user smith wants to display the total number of lines that are 4 characters (letters and digits)
long or more from the file1.txt file. Which regular expression or command should smith use?

A.
egrep “^[[:alnum:]]{4,}$” file1.txt | wc -l

B.
egrep “^[[:alpha:]]{4,}$” file1.txt | wc -l

C.
egrep “^[[:alpha:]]{4,}$” file1.txt | wc -w

D.
egrep “^[[:alnum:]]{4,}$” file1.txt | wc -c

Explanation: