Consider the regular expressions: R1 = (01)* (0*1*) (10)
R2 = (101)* (01)*
R3 = (10) (01*)*(01)
R4 = 10(R2*)|R3

Recall that, for a list of regular expressions, the function getToken() returns the next token from the input that matches one of the regular expressions. If there is more than one match, the longest match is returned. If there is more than one longest match, the token with the longest match that appears first in the list is returned. If there is no match, ERROR is returned. If the function getToken() is called once on input 1000101, it will return:

a. R1
b. R2
c. R3
d. R4
e. ERROR