The underlined sentence is ______________ of the following paragraph. "Gold, a precious metal, is prized for two important characteristics. First of all, gold has a lustrous beauty that is resistant to corrosion. Therefore, it is suitable for jewelry, coins, and ornamental purposes. Gold never needs to be polished and will remain beautiful forever. For example, Macedonian coin remains as untarnished today as the day it was minted twenty-three centuries ago. Another important characteristic of gold is its usefulness to industry and science. For many years, it has been used in hundreds of industrial applications. The most recent use of gold is in astronauts’ suits. Astronauts wear gold-plated heat shields for protection outside spaceships. In conclusion, gold is treasured not only for its beauty but also for its utility."
A、the topic sentence
B、the controlling idea
C、the major supporting sentence
D、the minor supporting sentence