根据短文内容，从下面方框中选择适当的单词或短语填空，使短文内容完整正确。

know          climate          stay off           took part        grown into

The lights in many buildings around the world were turned off at 8: 30 p.m. on March 29^th, 2014. The lights _____小题1:____ for one hour an event called Earth Hour. The event is organized by the World Wide Fund for Nature, also ____小题2:___ as the World Wildlife Fund. People are asked to turn off their lights for one hour to call attention to ___小题3:_ an international event. People in more than seven thousand cities in one hundred and fifty countries ___小题4:__ this year. The event organizers say big changes start with small steps like turning out the lights.

磨损现象是非常复杂的，是导致机械损坏的（）。

A.主要原因之一；

B.次要因素；

C.一般原因；

D.无关原因。