Why do teenagers go to sleep late according to Carskadon?

(单选题)The mobile phone ______ in 1973. (单选题)Lily is my classmate. We ______ each other since she came to (单选题)My mother ______ some washing when the telephone rang. (单选题)— How do you usually go to school?—I ______ to school on foo (单选题)—______ I hand in the report today?—No, you needn’t. (单选题)The hotel is very old. It’s one of ______ buildings in the c (单选题)—______ did you stop playing?—Because I was tired. (单选题)More and more young people go skating ______ winter. (单选题)My father is a worker. ______ is very kind. (单选题)In the author’s opinion, the four books ______.