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 hit later. By that time, Latin, Old Norse(the language of the Viking invaders), and especially the Anglo-Nor-man 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 from the twelfth century through the fifteenth. The influence of French(and Latin, often by way of French)upon the vocabulary continued throughout the period, the loss of some inflections and the reduction of others accelerated, and many changes took place within the grammatical systems of the language. A bypical prose passage, specially one from the later part of the period, will not have such a foreign look to us as the prose of Old English, but it will not be mistaken for contemporary writing either.The period of Modern English extends from the sixteenth century to our own day. The early part of this period saw the completion of a revolution in vowel distribution that had begun in late Middle English and that effectively brought the language to something resembling its present pattern. Other important early developments include the stabilizing effect on spelling of the printing press and the beginning of the direct influence of Latin, and to a lesser extent, Greek on the vocabulary. Later, as English came into contact with other cultures around the world and distinctive dialects of English developed in the many areas which Britain had colonized, numerous other languages made small but interesting contributions to our word-stock. What is the main feature of the grammar of Old English().

A. The influence of Latin.
B. A revolution in vowel distribution.
C. A well-developed inflectional system.
D. Loss of some inflections.