A:looked; were thinking
B:looked; had thought
C:were looking; thought
D:were looking; were thinking
某校化学兴趣小组就空气中氧气的含量进行实验探究:
【收集资料】硫是一种淡黄色固体,在空气中点燃时能与氧气发生反应生成二氧化硫(表达式:S+O2 点燃__ SO2),SO2是一种有刺激性气味的气体,易溶于水.
【设计实验】第一小组同学选择的药品是足量的红磷,设计如图1.