答案：C.
1.when引導(dǎo)一個(gè)時(shí)間狀語從句,翻譯：當(dāng)諾姆拜訪我家共進(jìn)午餐時(shí),他把他的假期照片給我看.
主從句成分齊全,為正解.
2.如果用which引導(dǎo)定語從句的話,則樓主需要明白這一點(diǎn)：
關(guān)系代詞（which等）必須代替先行詞（即被定語從句所修飾的名詞/代詞等）,并在定語從句中充當(dāng)一定的成分（如果主語/賓語等）.
which代指的先行詞就是his vacation photos,將其代入定語從句時(shí),它無法在從句中充當(dāng)成分,即his vacation photos不能和he visited my house for lunch放在一起構(gòu)成一個(gè)句子.
因?yàn)樵搹木浼炔蝗敝髡Z（he）,也不缺賓語（my house）.
3.還是給樓主看一個(gè)which引導(dǎo)定語從句的正確例句吧：
Norm showed me his vacation photos (which he had taken in Beijing).
其中,關(guān)系代詞which代指先行詞his vacation photos,在括號(hào)中定語從句中充當(dāng)taken的賓語.
即：which he had taken in Beijing
= he had taken which in Beijing
= he had take his vacation photos in Beijing
從句中含有一個(gè)固定搭配：take...photos,意思是“照相”.