产生IL-2的细胞主要为

A．B细胞

B．CD4⁺T细胞

C．CD8⁺T细胞

D．NK细胞

E．吞噬细胞

We climbed a tree, and all of a sudden it _______ to us that we were rather big to be up in a tree.    [ ]

A. struck        

B. lighted        

C. occurred        

D. came