若定义:float x;int a,b;,则正确的switch语句是()。
A. switch(x) { case1.0:cout<<"*\n"; case2.0:cout<<"**\n";
B. switch(x) { case 1.2:cout<<"*\n"; case 3:cout<<"**\n"; }
C. switch(a+b) { case 1.0:cout<<"*\n"; case 1+2:cout<<"**\n ";
D. switch(a+b) { case 1:cout<<"*\n"; case 2:cout<<"**\n";