我的作文,请问有哪些语法错误?（作文题目是What can we do to fight pollution）
内容：What can we do to fight pollution?First,we must put the rubbish into rubbish bins.Sencond ,we mustn't use too many plastic bags.Then,we must plant more trees.We must take a bus or ride a bike or walk to school.And we must close all the lights and fans when we leave a room.We must close all the windows when we use the air-conditioner.Let's try our best to fight pollution