Some students spend ________ time on the Internet. They forget to study, eat and sleep. They can't even communicate with people in real life.
A:too many
B:many too
C:too much
D:much too
设i为虚数单位,则5-i1+i=( )
频繁开关电视机,显像管里的灯丝很容易烧断.请问开和关电视时什么时候灯丝更容易断?说明理由.