1、句子成分分析：
【Peter主语 】【thinks of 谓语动词主体】【photography宾语】【 as谓语一部分】【 a career宾语】,【_one 作a career的同位语】【_（that 省略关系代词）he will never get bored with 定语从句】
2、这里按照所给选项,只能选A,one（=a career).这里标点符号是逗号,完全正确.
当然,也可以通过对比来理解这些正确变化：
①Peter thinks of photography as a career 【这里没有标点】【that/which ,或不填；限制性定语从句】_he will never get bored with
②Peter thinks of photography as a career【,】【one_同位语结构】he will never get bored with
③Peter thinks of photography as a career【,】【which引导非限制性定语从句】he will never get bored with
④Peter thinks of photography as a career【.】【That/It_is one】【that可省略】he will never get bored with
3、高考原题对比：
Meeting my uncle after so many years is an unforgetting moment,【one】I will never forget.