二尖瓣狭窄最常见的病因是

A．炎症
B．黏液样变性
C．退行性改变
D．缺血性坏死
E．创伤

Which of the following is NOT true of the Japanese language
a. It is divided into two types of phonetic alphabets.
b. It contains more katakana than hiragana.
c. Hiragana and katakana have the same number of sounds and characters.
d It includes Chinese characters.