题目

________ many times, but he still didn’t understand it. A. Having been told              B. Though he was told C. To have been told             D. He was told   答案：D植物体细胞杂交的最终结果是（ ）A.产生杂种植株B.产生杂种细胞C.原生质体融合D.形成愈伤组织