下列哪项是C纤维的生理特性

A．直径为2～5μm

B．没有髓鞘

C．末梢位于牙髓本质交界区

D．疼痛呈尖锐，快速，可以忍受

E．疼痛阈值低，在组织未损伤时即可兴奋

The two collections of poems written by William Blake, ______ and ______ hold the similar subject-matter, but the tone, emphasis and conclusion differ.

A. Songs of Innocence; Songs of Experience
B. Poetical Sketches; Songs of Innocence
C. Poetical Sketches; Marriage of Heaven and Hell
D. The Book of Urizen; The Book of Los