Louis Braille designed a form of communication enabling people to ______ and preserve their thoughts by incorporating a series of dots which were read by the finger tips.

A．retain

B．visualize

C．convey

D．transfer

接触过敏性皮炎致敏的抗原呈递细胞为（）。

A.棘细胞

B.角质形成细胞

C.颗粒细胞

D.基底细胞

E.朗格汉斯细胞