.some people who do not like to talk much are not necessary

.some people who do not like to talk much are not necessary shy;they------ just be quiet people
为什么 只能填may 不能填should

may (表示可能性)可能,也许
She may be a nurse.
她可能是个护士.
should (表示可能性、推测、推论或期待)可能,该
She should be here any minute.
她该马上就到.
Dinner should be ready by now.
此刻晚饭应该做好了.
两个的含义不同