科学家提出了一个新理论来解释恐龙灭绝的原因。

Scientists developed a new ___theory to explain the extinction of dinosaurs.

他们的训练计划基于最新的运动理论。

Their training program is based on the latest sports ___theory.

他的理论是早起能提高工作效率。

His ___theory is that getting up early can improve work efficiency.