what difficulty we had waling home in the snowstorm 是賓語從句,
從句里是主謂賓狀,
主語是we,謂語had,賓語difficulty,狀語(in) waking home in the snowstorm
由主干逐漸演化：
You can't imagine what difficult we had.
“我們所遇到的麻煩”
You can't imagine what difficult we had (in) walking home.
這里用的是固定結(jié)構(gòu) have difficult (in) doing ,省略了介詞 in,walking home 是從句中的狀語
“我們走回家所遇到的麻煩”
You can't imagine what difficulty we had (in) walking home in the snowstorm.
in the snowsorm 也是從句中的狀語
“我們在暴風(fēng)雪里走回家所遇到的麻煩”
類似地：
You can't imagine what I just saw!
what I just saw 是賓語從句,只不過結(jié)構(gòu)簡單些,what本身做從句里的賓語而不用于修飾名詞.