某元素原子的最外层电子数为次层电子数的3倍,则该元素原子核内质子数为
My friend showed me round the town, ______ was very kind of him.
They use computers to keep the traffic _______ smoothly.
If you leave the club, you will not be_____back in .
What I need is_____ book that contains ______ABC of oil painting.
Jenny nearly missed the flight______ doing too much shopping.