Which of the statements below are true? Which are false?

a. In polling, I/O devices set flags that must be periodically checked by the CPU.
b. When using interrupts, the CPU interrupts I/O devices when an I/O event happens.
c. The overhead of polling depends on the polling frequency.
d. Polling is often a viable option for slow and asynchronous devices.
e. Synchronous I/O cannot be done with interrupts.
f. User processes are always blocked during asynchronous I/O operations.
g. Traps are software-generated interrupts.
h. System-calls can be implemented using either traps or polling.
i. DMA usually improves the overall system performance.
j. DMA is necessary for asynchronous I/O transfers