Question

polymers used in industrial applications are weakened by environmental stress, mechanical fatigue, and unexpected damage. however, new types of polymers have been engineered to repair ______ aided by embedded microcapsules, such materials begin to self - heal. which choice completes the text so that it conforms to the conventions of standard english? a) themselves—upon fracture— b) themselves. upon fracture, c) themselves upon fracture. d) themselves, upon fracture,

Explanation:

The em - dashes in option A create an unnecessary interruption. Option B has a period after "themselves" which makes the second part "Upon fracture, such materials begin to self - heal" a bit disjointed. Option D has an unnecessary comma after "themselves". Option C is the most grammatically correct and smoothly flowing choice as it clearly states that the polymers repair themselves when they fracture.

Answer:

C. themselves upon fracture.