A:元素是具有相同核电荷数的一类原子的总称
B:元素周期表,元素的原子序数与该元素原子核电荷数在数值上相同
C:同种元素的原子核内质子数与中子数一定相等
D:在物质发生化学变化时,原子的种类不变,元素也不会改变
列举我国建国后的三项重大科技成果。
⑴What is this? ____ A. Thursday.
⑵What are these?____ B. Yes, it is.
⑶What is she wearing?____ C. They're shorts.
⑷Is this a new cap?____ D. She is wearing a blue skirt.
⑸What day is today?____ E. It's a new T-shirt.