They have been here once.把been换成came怎么样

They have been here once.把been换成came怎么样 They have been to Beijing only once. It's about three years since they＿here.是填came还是have been? they have been here since 2000 The work has been finished since they came here They have been attractions to tourist .能不能换成They have been a they have been here since 1988,对1988进行提问,（）（）have they been 1.They have been here since 2000.___ ___ They must have been here the day before yesterday,---------- Where have they been? He came here a year _______,and I have been here _______ two they have been to the summer palace only once（only once划线提问）