What is the main difference between the batch and at commands?

What is the main difference between the batch and at commands?

A.
The batch command will run multiple times.The at command will only run once.

B.
The batch command will run when system load is low. The at command runs at a specific time.

C.
The at command reads commands from standard input. The batch command requires a
command line argument.

D.
The at command e-mails results to the user. The batch command logs results to syslog.