— By asking the teacher for help.通过向老师寻求帮助。

点拨：①{#blank#}1{#/blank#}意为"为……而学习"。for为介词，意为"为了"，表示目的。

如：我为人民而学习。   {#blank#}2{#/blank#}

②by 为介词，意为"通过……方式"，后接名词，代词或动名词。

如：她通过听英语新闻来学习英语。 {#blank#}3{#/blank#}

Everyone should {#blank#}1{#/blank#}a {#blank#}2{#/blank#}in saving the earth.

I enjoy sports {#blank#}1{#/blank#} {#blank#}2{#/blank#}, especially tennis.

It's necessary to divide the waste into different kinds before we {#blank#}1{#/blank#}it{#blank#}2{#/blank#}.

Just {#blank#}1{#/blank#}! I'll be back soon.