下列气体,能使紫色石蕊试剂先变红后褪色的是( )
A:CO2
B:氯气
C:O3
D:SO2
已知等差数列an满足a2+a4=4,a3+a5=10,则它的前10项的和S10=( )
A good listener takes part in the conversation, ______ ideas and raising questions to keep the talk flowing.