一It's said that aliens tried to warn the astronauts on the moon to _____.

一Maybe they didn't like human beings to get close to them.[ ]

A.stay up

B.stay out

C. stay away

D.stay behind

下列各物质中，互为同系物的是

A．丙三醇和乙二醇

B．甲苯和苯乙烯

C．正丁烷和2，2-甲基丙烷

D．1，3-丁二烯和1-戊炔