iftheyknewhowdifficultitwastodrillthroughthehardrock条件状语从句
howdifficultitwastodrillthroughthehardrock宾语从句
itwastodrillthroughthehardrock中的it是形式主语
itwastodrillthroughthehardrock中的todrillthroughthehardrock是不定式做真正的主语,
theywouldloseheart是整个句子的主语
要是还有不懂的再问我