Is there any possible way to help them get rid of such a bad habit?— To tell the truth, it’s very hardBut weon this problem trying to improve the situation

Did youlisten to Mr.Jackson’s lecture — Yes，I have never heard a _____ one.

下边句子中加横线的熟语，能够替换为括号中成语的一项是（ ）

______useful dictionary for beginners ofEnglish! Where did you get it

Scientists are convinced_____the positive effect of laughter_____physical and mental health