①小勇缺乏自我保护意识

②小勇的行为违反了《教育法》和《义务教育法》的有关规定

③网吧老板违反了《中华人民共和国未成年人保护法》中的社会保护的规定

④小勇有上网的自由，但浏览不健康信息的行为是不对的

Can the little boy in a blue shirt over there ____ (stay) at home alone?

用所给词的适当形式填空 
The ruler____  (use) since I began my school life.
Tony didn't find____  (learn) English easy.
____ (compare) with Paris, London is larger.
My mother encouraged me____ (enter) the competition of this year.
His memory of the____  (please) trip will last long.

大气中有两种氧元素组成的单质，即氧气和臭氧（O₃）．在一定条件下，部分氧气转化为臭氧，下列说法正确的是（　　）