+(-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°