The correct option is
A provide support for an assertion made in the preceding sentence (lines
10−12)
In lines 10−12, the author asserts that child labor laws pitted women of different classes against one another. The view of the middle-class women reformers is stated, and then, to show that working-class mothers did not hold the same opinion, the author turns to the recent work of women historians to support this statement.
A Correct. The author uses the recent work of women historians to support the statement that women of different social classes were pitted against one another.
B The women historians have recently observed; the verb observed introduces a statement rather than a question.
C The reference to women historians has to do with working-class mothers; it does not challenge women's activism and role in social reform.
D The passage supports what the women historians say about working-class mothers.
E The author does not define or present the traditional view of child labor reform, nor is any inherent contradiction pointed out.
The correct answer is A.