Only ________ of the students come to school by bus.
A:three fifth
B:third fifths
C:three fifths
D:third fifth
①过点P作BC的垂线,D是垂足;
②过点P作BC的平行线交AB于E,过点P作AB的平行线交BC于F.
①发出明亮蓝紫色火焰的是____;
②产生大量白烟的是____;
③不属于化合反应的是____;
④生成黑色固体的是____.