___       is well known is that Africa had contacts with India and the Red Sea civilizations from the earliest times．

It is required that in no case ________ our password.

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

________ hard, and you will pass the final exam. 

—Were all the supplies for the people carried to the flood-stricken areas?—No,      only some of them      nearly all the roads there cut off.