阅读下面短文，掌握其大意，从每题所给的A、B、C、D四个选项中，选出最佳选项。
Last year, I was sent to work at an office near my mother's house. 1, I stayed with her for a month. During that time, I helped her out with the housework and the 2.
After a week, I started 3 the groceries were running out pretty quickly.4, I began observing what my mother did every day for two weeks. To my 5, I found she would pack a paper bag full of canned goods and 6 every morning at about nine. She took the food to the slums(贫民窟) and gave it out to street 7. I asked around and 8 my mum was popular in the area. The kids looked up to her as if she were their own mother. Then it hit me — why didn't she want to tell me about what she'd been doing? Was she 9 that I would stop buying the groceries if I knew the truth? When she got home, I told her about my discovery and 10 she could say something, I gave her a big hug and told her she didn't need to keep it a 11 from me. She told me that the 12 of the children lived with an old lady in a makeshift home while others 13 on the streets. For years, my mum had been helping out by 14 whatever food she could 15. I was so touched by how 16 she was. She used what was 17 for her to help others in need. And I was so 18 of her. I 19 to buy groceries for my mum. But now, I always add a(n) 20 bag for her other children.
五种溶液, 这种试剂是
