The answer would be D, abandoning young before eggs hatched, due to the fact that the eggs would probably fail to develop correctly as a result of improper care. The other choices would actually increase their chances of survival.
I believe the answer is the poles of the magnet.
13.4 billion years is 3 times of the half-life, 4.47 billion years. So the Uranium-238 will go through three times of half decay. So the remain percentage will be 50%*50%*50%=12.5%.
