Which of the following are true about Java identifiers. a
A Java keyword cannot be used as an identifier.
b
All identifiers must start with either a letter, the US currency character ($), or an underscore (_).
c
Identifiers are case sensitive.
d
After the first character, an identifier can have any combination of letters, numbers, or $ and _ characters.
e
All of these are true.
f
All of these are false.