I called on the doctor yesterday.
我昨天去拜訪了醫生。
I called at the doctor's yesterday.
我昨天去了醫務室。
He was called up at the beginning of the war.
戰爭開始時他就被征召入伍了。
He called on the workers to fight for their rights.
他號召工人為爭取自己的權利而斗爭。
I'd like to call on you this Sunday.
我想這個星期天來找你。