—Quite a lot of students failed in the math exam．

—Exactly．It is ____ their abilities．

A．within

B．over

C．against

D．beyond

急性疱疹性龈口炎的临床特征为（）

A.口腔黏膜出现成簇的小水疱

B.口腔黏膜上白色凝乳状的绒膜

C.口腔黏膜、手掌、足底出现水疱、丘疹等病损

D.口腔黏膜散在的溃疡

E.疱疹沿神经排列，不超过中线