Answer:
b. $2
Explanation:
a. 2A is not a valid variable because variable names cannot begin with a number.
b. $2 is valid because variable names can begin with $ or _ characters.
c. d+4 is not a valid variable because variable names can only contain letters, numbers, underscores, or dollar signs. (+) sign is invalid.
d. d 4 is not a valid variable because variable names cannot contain spaces.
