Final answer:
The correct word to complete the sentence about the mountain climber is 'sustained', which means to support life, particularly through food or drink. The correct answer is option B).
Step-by-step explanation:
The student's question involves choosing the best word to complete the sentence: 'Trapped by a storm, the mountain climber sustained himself for six days by filtering river water.' The correct answer is (B) sustained, which means to support life or keep alive, especially through food or drink. In the given context, 'upheld' is not the appropriate word because it usually refers to supporting something in a moral, legal, or intellectual sense. 'Persevered' means to continue in a course of action even in the face of difficulty but does not specifically imply maintaining life. 'Perpetuated' means to make something continue indefinitely, and it is not suitable for the context where a person is maintaining their own life.