太阳能是一种重要的可再生能源。

Solar power is a vital ___renewable energy source.

这份合同是可续签的，双方可以选择延长合作期限。

This contract is ___renewable if both parties decide to extend the cooperation.

太阳能是一种可再生的能源，因为它来自源源不断的太阳光。

Solar energy is a ___renewable resource because it comes from the continuous sunlight.