I just did a test (created by a non-native speaker) and there were these two questions in it:

1. The firemen were standing ________ in case there was an explosion.
a) by
b) back

2.The teacher told the kids to stand ________ so that they all could see the experiment.
a) around
b) back

I think that in both questions both choices are possible. The author of the test obviously didn't think so. What do you think?