He____ ____the mobile phone and passed it to me.
设{bn}是等差数列,b1+b2+b3=15,b3+b5+b7=33,Sn是数列{bn}前n项和,令Tn=4Sn+7bn若Tn≥a对一切的正整数n恒成立,则a的取值范围为( )
当晶体的温度正好是熔点或凝固点时,它的状态为( )