A:2x+y-1='0'
B:2x+y-5=0
C:x+2y-5='0'
D:x-2y+7=0
—I don't know. It ____ (mend) by my brother now.
原来大树上有35只小鸟,又飞来18只,现在有几只小鸟?
如图是氧化汞分子分解示意图.从示意图中,你能够得出的规律或者结论有:(答出两条即可)
①____.②____.