By三种用法三句1：2：3：It作形式主语1：Used to2:Be used to do3:Be used to do

1.被,由 The homework was assigned by the teacher.这些家庭作业是老师布置的.2.靠,用,通过 They crossed the river by ferry.他们乘渡船过了河.3.经由;沿 Ellen flew to Chicago by way of Minneapolis.艾伦经由明尼阿波利斯飞往芝加哥
used to表示过去常常做某事.
例句:I used to play football after school.过去我常常在放学后踢球.
be used to do的意思是被用来做某事;be used to doing的意思是习惯于做某事.
be used to 被用来做
used to + do："过去常常"表示过去习惯性的动作或状态,但如今已不存在.
Mother used not to be so forgetful.
Scarf used to take a walk.(过去常常散步)
be used to + doing：对……已感到习惯,或"习惯于",to是介词,后需加名词或动名词.
He is used to a vegetarian diet.
Scarf is used to taking a walk.(现在习惯于散步)