化学键按原子间的相互作用力的方式和强度不同，可分为（）和配位键。
A、共价键
B、离子键
C、电离键
D、金属键
参考答案：A, B
They _______ England and they will be back next week. [ ]
A. have gone to
B. have been to
C. have gone in
D. has been on
层序地层学
