原子一般由原子核和______构成,原子核一般由质子和______构成.
原子都是由原子核和核外电子组成的,而原子核还可再分为带正电的质子和不带电的中子.
故答案为:核外电子;中子.
-_______ busy schoolwork, the children also have to take arts, music and sports classes in their free time.
-I wonder what they will become.[ ]
A. Rather than
B. Owing to
C. Apart from
D. Except for
在病例对照研究中,若选用现患病例作为研究对象,最常见的偏倚是()
A.回忆偏倚
B.失访偏倚
C.入院率偏倚
D.易感性偏倚
E.现患病例-新病例偏倚