Do you know the _________ of the saying I just quoted?

At the meeting they discussed three different __________ to the study of mathematics.

Although Tan Weiwei began her_______by singing in a local Ear, she is now a famous star.(成都市)

In order to understand the____ of the animal, she spent many years recording its daily activities.

Many countries are increasing their use of natural gas, wind and other forms of ____.