What is independent clouse?

An independent clause is a clause that can stand by itself as a simple sentence. An independent clause contains a subject and a predicate and makes sense by itself. Independent clauses can be joined by using a semicolon or by using a comma followed by a coordinating conjunction.

Explanation:

the following key ideas correctly express the key sentence.

restate key idea: most people can learn to swim in ten short lessons.

restate key idea: the majority of water-accident victims require mouth-to-mouth breathing.

restate key idea: an empty, tightly closed gallon jug will support a tired swimmer.  

restate key idea: first aid is to prevent accidents as well as assist in rescue.

explanation: the key idea needs to have the same topic as the key sentence (drowning and safety).

a. inform

explanation:

"how to" tells us that it will explain how to, which means to inform