区别就是两者都是可以表示一般将来时，但betodo常用于按安排好的去做。其他具体的不同如下
be to do中文意思是打算做
The marsupial's eye problem may be to do with her diet before she was abandoned， or because she is overweight， leading to fat deposits behind her eyes.
willdo中文意思是会做的
It's amazing what some people will do for gain.
