Which of the following is not the reason that we need only one stack to evaluate a postfix expression:

a. Each operation is used as soon as it is read, so no need to use a stack to store operations.

b. Each number is used as soon as it is read, so no need to use a stack to store numbers.

c. When reaching an operation, its two arguments have been read and stored.

d. When reaching an operation, no operation after this operation needs to be used before this operation.