求助一道Prep的题

If x and y are positive integers such that x=8y+12, what is the greatest common disisor of x and y?
(1) x=12u, where u is an integer.
(2) y=12z, where z is an integer.
答案给的是B
我选的是E.
请帮我看一下，谢谢。

93. the lifetimes of all the batteries produced by a certain company in a year have a distribution that is symmetric about the mean m. if the distribution has a standard deviation of d, what percent of the distribution is greater than m+d?
(1)68 percent of the distribution lies in the interval from m-d to m+d, inclusive.
(2)16 percent of the distribution lis less than m-d
答案是D
为什么呢？
麻烦大家帮我看看
谢谢。