B let us check on the things we like to do on the internet.
check on检查
C Do you know the name of the person who sent you the e-mail?
who引导定语从句,同时在从句中作主语.
C We were just too tired to walk any further.
far的比较级是farther或further,前面不能再加more,因为加了more后重复了.
B I wish I could fly as high as a swan.
high可以作副词,但它指的是具体的高；highly指抽象的高,常译成”高度地“.
B What fun it is to talk to far away friends on a computer.
fun是不可数名词,前面要用what表示“多么”.