老师你好！
中国正在拓展公众可参加的项目。
China is developing some programs in which the public can take part in.
如此翻译对吗？
这是 in which 引导的定从，可以用that吗?
最后 take part in 的 In 需不需要去掉？
介词既能够放在关系代词的前面（比较正式），也可以放在关系从句的末尾（较不正式）。
......
This is the room in which I was born. 这就是我生的房间。（正式）
This is the room I was born in.这就是我生的房间。（非正式）
who 和 that 不需要在介词后面。
（以上内容摘自《牛津英语使用方法指南》第三版498.7节）
This is the roomI was bornin.这就是我生的房间。（非正式）
也就是说，介词在句末时，关系代词可以用which或者that，也可以省略关系代词；介词用在关系代词前面时，只能用which, 不可以用that。
所以：China is developing some programs in which the public can take part in. （错误）China is developing some programsin thatthe public can take part. （错误）
China is developing some programs in which the public can take part .（正确）
China is developing some programs which the public can take part in.（正确）
China is developing some programs that the public can take part in.（正确）
China is developing some programsthe public can take partin.（正确）
