—The land in the southwest of China is in great need of .—Yes, it hasn't rained for a long time there.
A:people
B:food
C:water
①用DNA分子探针诊断疾病
②快速灵敏地检测饮用水中病毒的含量
③B淋巴细胞与骨髓瘤细胞杂交
④目的基因与运载体结合形成重组DNA分子.