V mL Al2(SO4)3溶液中含Al3+a g,取mL溶液稀释到4 V mL,则稀释后溶液中SO的物质的量浓度是( )
It is often ______ that human beings are naturally equipped to speak.
I can’t leave. She told me that I ______ stay here until she comes back.
—— Do you mind my opening the window? It’s a bit hot in here. —— ______ , as a matter of fact
It’s high time you had your hair cut ; it’s getting _______ .
My friend showed me round the town, ______ was very kind of him.