慢性铅中毒引起的肠痉挛属于（）。

A.机械性绞窄性肠梗阻 

B.机械性单纯性肠梗阻 

C.麻痹性肠梗阻 

D.痉挛性肠梗阻 

E.血运性肠梗阻

Paul started hiking in 2010 and he has hiked across 11 countries ______.

[      ]

A. ever since

B. from then on

C. right away

D. at once