It's always helpful, for starters, to be sure you have a sense of the main point of a Reading Comprehension passage, and the point of each paragraph. Here, the first paragraph sets out a problem ("conventional full-time workdays . . . are too inflexible for parents with primary child-care responsibility"). The second paragraph clarifies who bears the brunt of this problem ("barriers against successful participation in the labor market that are related to primary child-care responsibilities mainly disadvantage women"). The third paragraph talks about compromises working mothers are forced to make, and cites as a specific example part-time work, which is juxtaposed with full-time work. The fourth paragraph delves deeper into the compromises working mothers must make.
The question here asks you what "can be inferred" - i.e., what Must Be True - about part-time work, based on the information presented in the passage. So you are looking for the answer choice that is textually-supported. You know that part-time work is discussed in paragraph 3, so you should focus your attention there.
Answer choice (A) is wrong because there is no textual support for the claim that one-third of all part-time workers are working mothers. Be very careful here. The passage says something different: "one-third of all working mothers are employed only part-time." (Lines 28-29).
Answer choice (B) is wrong because the drawbacks of part-time work explained in the passage - "even though part-time jobs are dramatically underpaid and often less desirable in comparison to full-time employment" (Lines 29-32); "usually available only in occupations offering minimal employee responsibility and little opportunity for advancement or self-enrichment" (Lines 33-35) - do not apply differently or more "to working mothers than to women generally."
Answer choice (C) is wrong because there is no textual support for this claim, which is just not discussed in this passage.
Answer choice (D) is correct. The textual support is at lines 36-39: "such employment does allow many women the time and flexibility to fulfill their family duties, but only at the expense of the advantages associated with full-time employment."
Answer choice (E) is wrong because there is no textual support for this claim, which also is just not discussed in this passage.
