单项选择题
A．has nothing to do with heredity B．is not known by scientists C．has little to do with the working of their brains D．is that left-handers are mainly twins
A．few are men B．most of them are women C．half of them are men D．two thirds are men
A．If both parents are left-handed, about 50% of their children will be so. B．The greater part of left-handers have right-handed parents. C．One in ten of Americans are left-handed. D．Most of us will favor the right.