A train operator should know that the automatic stop mechanisms used on the subway system are designed so that in case of signal power failure the stop arms will automatically move to the tripping position even though the locks ahead are clear. This is done because:
a. It is safer to have the stop arms in tripping position when signal power fails.
b. It allows faster operation of trains during signal power failures.
c. The stop arms are less likely to function during power failures.
d. Tripping position improves signal visibility during power failures.