It is _________ difficult work that we can't finish it in a short time.

A．so a

B．such a

C．so

D．such

下列哪项不是维生素D缺乏性佝偻病初期的临床表现（）

A.易激惹

B.睡眠不安

C.多汗

D.枕秃

E.惊厥