Among them will be her mother,who swam the Channel ( ) when she was a girl

问题描述:

Among them will be her mother,who swam the Channel ( ) when she was a girl
这是一篇短文中的一句,请回答并解释,
a.just
b.itself
c.so
d.herswlf

选d.
语意为在他们当中将会有她的母亲,她母亲很小的时候就独自游过了那条海峡