最常见的21－三体综合征的核型分析是（）
A.嵌合体型
B.D／G易位型
C.G／G易位型
D.标准型
E.白血病
参考答案：D
______ provided the methodological foundation for materials for the teaching and its principles formed the basis of such widely used series as English 900 and Success With English.
A. The Direct Method B. The Oral Approach C. The Audiolingual Method D. The Communicative Approach
农田中风速在株间变化呈（）分布。
A.指数型
B.对数型
C.“S”型
D.直线型
