Circus tigers, although they have been tamed, can _____ attack their trainer.

Trees need water to grow; _____, friendship needs our heart and passion to develop.

Although China has developed its economy greatly, its per capital GDP is still         one-tenth of the United States.

If we work with a strong will, we can overcome any difficulty, ＿＿＿great it is. 

The situation is very serious, even if the government tries to pretend ______.