A:①②④
B:①③④
C:①②③
D:②③④
同温同压下,体积比为3:2的H2和CO,它们的物质的量之比是____,原子个数之比是____,质量之比是____,密度之比是____.
Look at the books in the library.
____
—Why didn't you buy any bread?
—Sorry, I .