古代大臣上朝时手上拿着的狭长笏板，最初的用途是什么？
参考答案：最初的用途是用来记事。
如果|a+2|+（b-3）2=0，那么2a-b=______．
Some people are worrying about the possibility ________ mobile phones could be responsible for a range of illnesses, from rashes(皮疹) to brain tumors．
A．that
B．why
C．how
D．whether
