转速单位是（）单位制。
参考答案：国家选定的非国际
把（+1）-（-6）-（+2）+（-9）写成省略加号的和的形式为______．
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
