最常见的这类比较是:If B can (do) .,why can't - Tom,it's time for school! - I don't wanna go,mom.It's snowing. - Sarah is already out there.If she can go to school today,why can't you? 这类表达方式还有多种,要根据不同的语境使用: B can do it,why can't If B can do it,A can,too. Even B can do it,why can't B can do it,but A can do better. .