This一般用于近指,一般是补充上一句的句子,或者说明一种情况和一种事物,就用This,This是These的单数形式,有时This和The比较难选择.
eg:Airflightwoulddelayduetothebadweather,thisiscommonlyseen.
That一般用于远指,定语从句,状语从句等等从句需要用That来联接.
eg:WehaveahopethatpeoplelandedinMalaysiaAirlinesFlightMH370stillbealiveandwillcomebacksafely
It一般指动物罗,有时同位语从句一般用It开头
eg:Itisafaith/wish/belief/(theway)that.