Fill in the blanks with the words given in A, B, C or D to complete the following passage

Hi, Lan. How are you? I’m happy to share with you some good news about my village. There have been some changes (24) _________ your visit last year. Last week I came back to my village and was really surprised. You know what? The lake is not (25) __________ any more. The factory has installed a new filtration system to treat the (26) _________________ waste. I saw lots of small fish in the lake and wild ducks swimming in the water. Besides, they have planted trees around the factory to reduce air pollution.

Since some villagers are in the habit (27)________ littering, people have placed dustbins in various places. This has resulted in a much cleaner environment. My grandparents say that at weekends the villagers also go around the village together to (28) ___________ rubbish. What about your neighbourhood? Tell me all about it in your next email.

Câu 24 : There have been some changes (24) _________ your visit last year.

A. for

B. since

C. after

D. before