I called on the doctor yesterday.
我昨天去拜访了医生。
I called at the doctor's yesterday.
我昨天去了医务室。
He was called up at the beginning of the war.
战争开始时他就被征召入伍了。
He called on the workers to fight for their rights.
他号召工人为争取自己的权利而斗争。
I'd like to call on you this Sunday.
我想这个星期天来找你。