Had a kind of tricky listening task with multiple choice.
Here it is:
A buoyancy control device helps the diver to …
1) control distance and depth.
2) fight decompression sickness.
3) regulate the air tank level.*
Barbara: ... Divers wear a BCD or buoyancy control device to control how much they float or sink. A pressure gage devise tells divers how much air is left in the air tank. Or a dive computer can calculate how much air is left as well as the diver’s depth and the length of time they can stay underwater. Scuba divers breathe with the regulator which brings air to the mouth when they inhale. The regulator is attached to an air tank that is placed on the diver’s back. There is also an extra regulator called an octopus. It’s used in case of the emergency situations.
Presenter: I know decompression sickness is a great problem for divers.
Barbara: You are right. It is a major concern for divers. The deeper a diver goes, the more pressure the surrounding water puts on the volume of the air inside his or her lungs. And the deeper a dive the more nitrogen gas goes into the diver’s blood.
There are no official keys to it, but most of my Russian colleagues think that the 1st answer is correct. Sure, BCD deals with depth, but nothing was said about distance. So, I can't fully agree with them.
I'm inclined to think that the correct answer is the 2nd. It's because decompression sickness is related to the depth a diver goes to. The only thing I'm not sure about is the verb 'fight'. BCD doesn't really fight the disease. It helps in some sense to control the depth and avoid the disease.
Sorry for such a long description of the matter:) As native speakers, could you help me to choose the right answer.