Language points
①. call up 打电话，使......回想起  I’ll call you up tonight (call sb. /ring sb. up )  The old photo calls up memories of my   childhood. (recall sth.)   call for 需要, 要求      call off 取消   call in 邀请, 请来  call on/at 造访 (call on后跟人作宾语，call at后跟地点名词作宾语 )
            call on            drop in on            pay a visit to            go on a visit to                       visit
造访某人
+ sb.
造访某地
call at drop in at pay a visit togo on a visit to visit
+sp.