_______ is known to all，China will be an _______ powerful country in 20 or 30 years’ time.
C
as可以用来引导一个非限制性定语从句，通常无明显的先行词。as指代的是主句陈述的内容。而as引导的从句既可以放于句首，也可以放于句末或句中。
Shouldyourprice______reasonable,wewillplaceanorder______you.
Touristexpenditureshavedifferenteffectsonadestinationeconomy:salesbyfoodvendorstorestaurantsare_______effect;whiletaxifaresandairlineticketsalesare_______effect.
WearegladtoreceiveyourtelegraphicorderofMay6,______regretthatwecannotsupplythegoods______theendofMay.
AfterI_________aletterItookhertoa__________________.