(2012·安徽) The limits of a person's intelligence, generally speaking, are fixed at birth, but __________ he reaches these limits will depend on his environment.
She pretended ________the letter I wrote the day before yesterday.
Our father often told us in the past that _____is believing.
Is______necessary to change trains at Beijing?
When and where to build the new power station ______ yet.
_____is a good of exercise for both the young and the old.