A:was the mountain climber rescued
B:that the mountain climber was rescued
C:when the mountain climber was rescued
D:then the mountain climber was rescued
①HF、HCl、HBr、HI的热稳定性依次减弱
②NH3易液化
③F2、Cl2、Br2、I2的熔、沸点逐渐升高
④H2S的熔、沸点小于H2O的熔、沸点
⑤NaF、NaCl、NaBr、NaI的熔点依次降低
在△ABC中,AB=AC,AB的中垂线于AC所在的直线相交所得的锐角为40°,则底角∠B的大小为____