He didn't _____ to what I said because his mind was on something else.
A:hold on
B:take in
C:catch on
D:get over
____ ____you ____ at seven o'clock last night?
如图是实验室常用的装置,请据图回答:(1)写出仪器①的名称____。在实验室收集二氧化碳气体一般只用D装置,由此推测二氧化碳气体具有的性质是____;(2)用高锰酸钾制取较为纯净的氧气的装置组合是____(填序号);(3)若收集一瓶氧气供硫粉在氧气中燃烧的实验使用,最好选用气体的收集装置中的____(填装置序号),理由是____
若α为锐角,且cosα=45,则tanα为( )