Mrs. White became a teacher in 1985. She _____ for twenty years by next summer.

A．will teach

B．would have taught

C．has been teaching

D．will have been teaching

物质的紫外吸收光谱反映了物质分子中生色团和助色团的特性，可利用这些特征对于在紫外区有吸收的待测组分进行结构分析和定性。