+（-3）=-3，
-3的相反数是3．
故选：C．
The rescue team has saved more than ten people________under the collapsed buildings since the earthquake occurred in Ya’an.
A．trapping
B．to be trapped
C．trapped
D．having trapped
如图所示，空气中有一块横截面呈扇形的玻璃砖，玻璃砖的折射率为2．现有一细光束垂直射到AO面上，经玻璃砖反射、折射后经OB面平行返回，∠AOB=135°，则光线在OB面上的入射角应是（ ）
A．15°
B．30°
C．45°
D．60°
