Helen is going to work in an old people's home to help ________ the old people.
A:look forward to
B:look after
C:look through
测得生活中一些液体的pH如下表:
液体
雨水
糖水
厨房清洁剂
厕所清洁剂
pH
5.6
7
11.8
2
下列有关监测和预防遗传病的做法,正确的是( )