It remains to be seen________North Korea will remain stable under its new young leader.

—You look unhappy， my son?—I’m wondering how long it’ll be          we come to China again.

There is no doubt ________ those who work hard will succeed sooner or later.

---It’s burning hot today, isn’t it?       ----Yes. ________ yesterday.

The more one is _______ the English-speaking environment, the better he or she will learn the language.