[单项选择]两栖动物成体的肾脏类型是（）。
A. 原肾
B. 前肾
C. 中肾
D. 后肾

The history of English is conventionally, if perhaps too neatly, divided into three periods usually called Old (or Anglo-Saxon)English, Middle English, and Modern English. The earliest period begins with the migration of certain Germanic tribes from the continent to Britain in the fifth century A. D, though no records of their language survive from before the seventh century, and it continues until the end of the seventh century or a bit later. By that time, Latin, Old Norse(the language of the Viking invaders), and especially the Anglo-Norman French of the dominant class after the Norman Conquest in 1066 had begun to have a substantial impact on the vocabulary, and the well-developed inflectional (词尾变化的) system that typifies the grammar of Old English had begun to break down.
The period of Middle English extends roughly form the twelfth century through the fifteenth. The influence of French(and Latin, often by way of French)upon the vocabulary continued throughout the pe
A. The influence of Latin.
B. A revolution in vowel distribution.
C. A well-developed inflectional system.
D. Loss of some inflections.