Scientists are convinced________the positive effect of laughter_______physical and mental health.   [     ]

 A. of；at          

B. by；in    

C. of；on    

D. on；at

胰腺癌最常见的临床表现为（）

A.腹痛，黄疸，消瘦

B.腹痛，休克，黄疸

C.腹痛，腹胀，呕吐

D.腹痛，寒战高热，呕吐

E.消瘦，便秘，呕吐