当事人订立的合同被确认无效或者被撤销后当事人的权利和义务（）。
A.结束
B.不完全结束
C.待定
D.执法部门决定
参考答案：B
If a three-digit number is selected at random from the integers 100 to 999, inclusive, what is the probability that the first digit and the last digit of the integer will both be exactly two less than the middle digit ？（）
A. 1:900
B. 7:900
C. 9:1,000
D. 1:100
E. 7:100
