Why can a decline in infant mortality have a double effect on population growth?

Correct answer: More children survive and family planning thinking may also change

Direct answer: B is correct. When infant mortality declines, more babies survive into childhood and later adulthood, so the population receives a direct increase in survival. It may also influence family decisions: when parents become more confident that their children will survive, they may gradually prefer smaller families, which can reduce births in the longer term. Thus the change can have two connected effects—more children surviving now and possible changes in desired family size later. B is correct because it includes both effects without claiming that the second effect happens instantly or identically everywhere. A is the opposite of the fact. C is wrong because lower infant mortality means fewer infant deaths, not an automatic rise in death rate. D is wrong because mortality and migration are different processes. Memory cue: better survival adds people first and may alter fertility choices later.