Lifeguards are likely to be outdoors at the beach or the outdoor public pool. Though some public pools are indoors.
Lawyers will often be in courthouses or their office, so choice A is out.
Engineers will likely be in their offices as well behind a desk working on a computer to design their latest object (eg: a bridge for instance). So choice C is out.
Pilots will spend all of their time in the air, so choice D is out also.
