27. The boy gathered all his _____ to stand up.
If we ___________some measures, we might have prevented the environmental pollution.
Many Chinese universities provide scholarships for students _____financial aid.
Scientists are convinced _____the positive effect of laughter _____physical and mental health.
Could you give me a hand? It seems that my strength has _________.
Unfortunately, ____ stone hit him on ______ head and he got injured.