Diving In (19) There are also diving jobs that can involve some danger. (20) One of these is water-tower diving. (21) The water towers that supply our communities with drinking water requires regular maintenance. (22) The outsides of these tanks are manageable enough, but professional divers must be hired to inspect, clean, and maintain the insides of the tanks. (23) The divers have to climb more than 100 feet up a tower and then descend into very dark and often cold water. (24) And because the tanks are usually operating at the same time, the divers must be very careful when they are inside. How should sentence 24 be changed?