You can use to respond to problem-and-solution essay test questions
a.
your writing portfolio

b.
the writing process

c.
peer review

d.
interviews

You can use the writing process to respond to problem-and-solution essay test questions. Option B is correct.

In problem-and-solution essays, the students need to discuss the problems with pertaining to a particular topic and then suggest possible solutions to these problems. The first fundamental step is to spot one of these questions when it arises.  

Problem solution essays are usually a type of essay question given in exams.

your answer is c) experiments with water vapor showed that elements combine in specific proportions.