a) The ancestor language of Modern English, also called Anglo-Saxon, spoken in Britain from about 400 AD to 1100 AD. The language is a more inflected language, maintaining strong and weak verbs, nouns, and adjectives. It has a clearly marked subjunctive mood, and has 5 cases of nouns and adjectives. In addition to singular and plural grammatical numbers, there was a dual number for two people. After ca. 884, many Old Norse words made their way into Old English, as Norse settlers in the Danelaw interacted with native Anglo-Saxons.
b) Middle English.
Wikipedia foundation.