【正确答案】 B

【答案解析】[解析] now and then：时而，偶尔。occasionally：时而，偶尔。always：经常。we have always done it in this way．我们经常这么干。constantly：不断地。She is constantly changing her mind．她老是改变主意。注意：动词进行体跟constantly，always等表达“反复”意义的副词搭配时动词动作具有反复性。这种搭配表达说话人对某人的某种行为的不满，具有强烈的感情色彩。下面这句话是不带感情色彩的客观报道：She constantly changes her mind．她常常改变主意。regularly：经常地；定时地。We do meet now and then，but not regularly．我们确实偶尔见面，但不经常。