完型填空。阅读下面短文，掌握其大意，然后从以下题所给的A、B、C、D四个选项中，选出最佳选项。
You may think there is only sand in the desert of the world, __1__ it is not true. In the desert, as we know, there is a little __2__, but it is not __3__ for most plants. Still we can see some plants __4__ in the desert.
