Answer:
constant or constant expression
register name
variable name (memory)
Step-by-step explanation:
Literally, operand means data which an operation can be performed on. The operation could be an arithmetic or logical operation.
From the list of options, several operations can be performed on:
- constants e.g.

- registers and
- variables e.g. (a + b)
However, no operation can be performed on keywords and/or reserved words.