下列婚配方式中，后代患遗传病的可能性最大的是

A．南方人和北方人

B．同一姓氏的人

C．表兄妹或表姐弟

D．生活在同一地区的人

—We were surprised to hear that the reason_______ she gave for her absence was______ her mother was ill.

—Yes，we saw her mother was at the supermarket that morning.

A．why；that

B．which；that

C．that；because

D．why；because