economic theory
經濟理論
scientific theory
科學理論
Darwin's theory of evolution
達爾文的進化論
He has a theory that the hole was caused by a meteorite.
他認為那個洞是隕石墜落形成的。
In theory, the journey should take three hours, but in practice it usually takes four because of roadworks.
按理說,行程應該只要三小時,但由於道路施工,實際上通常會需要四小時。