I believe the contrast between the words serves to show:
D. The author admires the Curies' ability to do important work in poor conditions.
Explanation:
The author talks of a "dilapidated stove" that the Curies used in their lab right before mentioning the "precious and exciting load." The contrast those adjectives being used in such proximity create is great. These are the Curies we are talking about; the amazing scientists behind the discovery of radioactivity. Yet, they needed coal for their dilapidated stove. Their being able to do such important work in such poor conditions is almost impossible to not admire. That seems to be the reason why the author has created the contrast by using those adjectives. The author admires their ability and wants us to do the same.
