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 commands of a batch job run sequentially one after another while the commands in at jobs may run in parallel.
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.