Manufacturers of writing paper need to add mineral "filler" to paper pulp if the paper made from the pulp is to look ...

Skylar on January 26, 2020

@shafieiava, happy to help.

Yes, the question stem "assumption on which the argument depends" indicates that this is a Strengthen with Necessary Assumption question.

Let's review what the passage tells us:
P: In order to make writing paper look white rather than gray, filler needs to be added.
P: Making white writing paper from recycled paper requires more filler than does making white writing paper from other sources.
C: Excluding the possibility that ways to use filler more efficiently or to whiten paper without filler are developed, manufacturers will have to use more filler than they currently do if recycled paper replaces other sources of writing paper.

The gap in logic here is that the conclusion never explicitly states that the paper has to be white. It is true that manufacturers would have to use more filler than they currently do to replace writing paper made from various sources with WHITE writing paper made from recycled paper, but this restriction is never specified. The correct answer will highlight this by showing that recycled paper can replace other sources of writing paper without causing more filler to be used- namely if that paper is gray.

(C) states "Grayish writing paper will NOT be a universally acceptable alternative to white writing paper." We can test this answer choice by negating it and checking to see if it makes the logic in the passage fall apart. When negated, (C) reads "Grayish writing paper WILL be a universally acceptable alternative to white writing paper." If gray paper is acceptable, then filler used to whiten the paper is unnecessary, meaning that recycled paper could replace other sources without causing more filler to be used. Therefore, (C) identifies the gap in logic stated above and makes the passage fall apart when negated, so it is correct.

(D) is incorrect because it is irrelevant. Even if there was a point of diminishing returns where adding filler could only make paper- regardless of source- so white, we know that recycled paper needs more filler than does other sources. Nevertheless, this does not matter because it does not address the gap in logic - the concept that the paper does not have to be white at all.

(E) is incorrect because it is unnecessary. Even if paper production levels stayed the same and only the source changed (so that recycled paper replaced other sources of writing paper), more filler would need to be used to whiten the paper. Therefore, negating (E) does not change the passage in any way.

Does that make sense? Please let us know if you have any questions!