supposed.
原因：be supposed to 的用法
用法一： be supposed to... 其中to是动词不定式符号,不是介词,其后要跟动词原形.当be supposed
to... 的主语是“人” 时,意为“应该……
”；“被期望……”,它可以用来表示劝告、建议、义务、责任等,相当于情态动词should.如：
Everyone is supposed to wear a seat-belt in the car.
每个人在汽车里都应该系安全带.