2004年6月18日，出现了百年难遇的天文奇观“金星凌日”，它是由于金星运行到地球与太阳之间，地球上的人们可以看到一个小黑点从太阳的表面移过，这个神奇现象的原理与日食相似，是由于光的______而形成的．
当金星转到太阳与地球中间且三者在一条直线上时，在地球上看到金星从太阳面上移过，这就是“金星凌日”现象，成因是光的直线传播．
故答案为：直线传播．
假如你是一位youth worker，一位名叫Simon的初三学生给你来信倾诉他的烦恼，内容见下表。请据此给他写一封回信，提出针对性的建议（表中建议可供参考），要求不少于80词，信的开头和结尾已给出，不计入总词数。
Thank you for your letter. I hope I can offer you some useful advice. I don’t think it’s wise to spend too much time watching TV and playing computer games. ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ______________________________________________________________________ I hope my advice will be of some value to you. Bill Smith |