1.the old是表示一类人,后面跟的动词应当为复数形式.Will you help the old when they fall down on the street?
2.percent的正确用法应该是 eighty percent of people,要加of.
3.because they think save life is first从语法上说并没有错,但是这么说比较累赘.整段话可以改为A recent survey from our class meeting shows that eighty percent person think they will help the old as much as they can,because saving life is the first,注意加the.
4.don't must是错误的,must的反义词应该是 don't have to.“视情况而定”应该是it will depend on the circumstances.
5.Last fifth precent person think they don't help the old这句应该用won't而不是don't,因为这是问在一个假设的情形下你会怎么做,用won't更合适.don't understand first aid也是错的,表示会某一种技能或某一种知识可以用know,此处应该是know nothing about first aid.“担心会惹上麻烦”可以说"express worry about getting into trouble".
6.一方面.另一方面.应该是on one hand.on the other hand. “I think help the old ,we will in a merry mood.”有两个主语了,这是错的. “we will be in a merry mood if we help the old”,当然也可以用别的说法.
7.help the old is help ourself,too.是错的.要用helping.如果你想表达“帮助别人也是帮助自己”,这个“也”不可以用too,而应该在句子中间用also,“is also helping ourselves". too是用于两个语义相同的句子的并列.I like apples. He like apples,too.