Walk on _______the traffic lights ,you'll see the post office on your left.

第一句across可以.
第二句,可以填below,through,above或者不填.
1.The plane is flying below the clouds.
飞机在云下飞行.
2The plane is flying through the clouds.
飞机正穿过去层.
3.The plane is flying above the clouds.
飞机在云上飞行.
4.The plane is flying the clouds.
一架飞机在云上面飞.