1.The night,during (这是定语从句,填关系代词 which,指代先行词 night) it rained,was very dark
2.What's the man about （关系代词 whom,指代先行词 man,这里作介词宾语）we know little
3.The train （乘火车是 on the train,所以这里用 on which）I travelled last year is very modern
4.The first photo(用关系代词 that 或省略（因为作宾语）,注意：由于先行词 photo 被序数词 the first 修饰,不能用 which)I took was when I was live
5.The chilren are playing in the park (这里指在公园里,用 where 指代 in the park ) here are many flowers
6.I lost my wallet,（意思是在钱包里,所以用 in which）there is ten yuan
7.The letter (which 和 that 都可以,由于作 received 的宾语,还可以省略) I received from my friend arrived yesterday
8.The building （which,指代先行词 building）stands there is our school
9.Do you know the man （whose,指代这个人的） beard is long?（原题有错,只好改正回答）
10.He is the very man （who,指代先行词 man,作主语） knows the news