题目

About one fourth of the families in the city have private cars and this number _____ to double in five years.   A. is expecting     B. has expected       C. is expected  D. will expect 答案：C等质量的氧化铜分别被氢气、碳、一氧化碳还原，则氢气、碳、一氧化碳的质量比是 [　　] A．1∶12∶28 B．2∶12∶28 C．1∶6∶28 D．2∶6∶28