A:3 hours’ ride
B:3 hours’ walk
C:3 hours’ flight
D:3 hour
晴朗的夜晚,我们用肉眼观察下列各种天体的感觉,叙述正确的是( )
I am……I can……I like……I'm good at……
My name is Lisa. I'm tall and thin. I can read and write. I like Chinese very much. I am good at writing. I want to be a Chinese teacher in the future. I want teach children in a school. I love children.
某元素氧化物的化学式为R2O5,其中氧元素与R元素的质量比为40:31,则R2O5的相对分子质量为 ( )