将5mol/L的Mg(NO3)2溶液a mL稀释至b mL,稀释后溶液中NO3-的物质的量浓度为( )
Charles was alone at home, with_______ looking after him.
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 _______ .