请教一道数学题

ashleyker

报了GWD的班，拿到的资料里有一本白皮数学，上面有一题：
An even number x divided by 7 gives some quotient plus a remainder of 6. which of the following,when added to x,gives a sum which must be divisible by?
a.1 ；b.3 ；c.7  ；d.8 ； e.13

答案是d。但是为什么a不对呢？

ashleyker

没有人知道吗？