The substance that can activate a large number of T cells to produce immune responses at very low concentrations is called（）
A. autoantigen
B. allergen
C. common antigen
D. superantigen
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Bound morphemes include____（）
A. bound roots
B. inflectional morphemes
C. affixes
D. free morphemes
In which period did Geoffrey Chaucer live（）
A. Old English
B. Middle English
C. Early Modern English
D. Late Modern English
Morphemes can be classified as_____（）
A. bound morphemes and free morphemes
B. inflectional morphemes and derivational morphemes
C. bound roots and affixes
D. prefixes and suffixes
Norman Conquest happened in the period of______（）
A. Old English
B. Middle English
C. Early Modern English
D. Late Modern English
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