谁能帮俺分析一下这个句子?请教大家哈

谁能帮俺分析一下这个句子?请教大家哈这句:When you visit london, one of the first things you will see is Big Ben, the famous clock which can be heard all over the world on the BBC. 请问,“when you visit```"这一句,是时间状语从句吗? “the famous clock```”这句对“big ben”的解释算什么呢?同位语从句还是什么啊?