题目

Comrade Li Dazhao, _____ librarian of Beijing University, was one of the founders of the Chinese Communist Party. A. sometimes B. sometime  C. some time  D. some times   答案：B钛酸亚铁（FeTiO3）可用来冶炼金属钛（未来将替代钢铁），其中钛元素的化合价是A．﹣4 B．﹣2 C．+4 D．+2