400-600-1123
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答案：
D
设只选修化
学的人数为A，只选修生物的人数为B，两门都选的人数是C，两门都不选的人数是D。则按照题目条件可以列式：
A+C=130 ——①
B+C=150 ——②
A+B+C+D=200 ——③
①+②：A+B+2C=280 ——④
④-③：C-D=80 → C=80+D
又因为D≥30，则C≥110，即，两门都选的学生最少有110人。
而又因为其代表了两门都选的学生，最大值的情况即A=C，A是B的子集，所有选化学的都选了生物，但选了生物的不一定选了化学。因此C≤130
综上：两门都选的人数取值范围为110 to 130。 
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