The past is always tense, the future perfect.

生命太短暂，不能浪费在糟糕的书上。

Sustainability is not an option; it's a necessity for the future of agriculture and food production.

Sometimes we get sad about things and we don’t like to tell other people that we are sad about them. We like to keep it a secret. Or sometimes, we are sad but we really don’t know why we are sad, so we say we aren’t sad but we really are.