retaining variety

例句：

1. 1. The farmer carefully retains the best varieties of wheat for the next season.
   农民小心地保留下季最好的小麦品种。
2. 2. The breeder is trying to retain the traditional characteristics of the breed.
   育种者正试图保留该品种的传统特征。
3. 3. The research team has identified several new retention varieties that could increase crop yields.
   研究小组已经识别出几个新的保留品种，这些品种可以提高作物产量。