He thinks he can do if he his best.

The _______ documentary describes _______ in the future.

（湖南省怀化市2014年高三第二次模拟考试）24My mother _____ all the cleaning for my family, but recently she has been too busy teaching to do it

The BRICS countries have____ to be a source of global economic development and essential to generations.

He promises ________ his old friend when he stays in Tianjin.