if they knew how difficult it was to drill through the hard rock,they would lose heart.这里为什么要加it,其什么作用

If They Only Knew 歌词 If they knew how difficult it was to drill through the hard rock,they would是虚拟语气吗 if they knew how difficult it was to drill through the hard rock,they would lose heart.这里这里it后面为什么加was if they knew how difficult it was to drill through the hard rock,they would lose heart.这里为什么要加it,其什么作用 if they knew how difficult it was to drill through the hard rock,they would lose heart请帮我分析下这段话的语法结构. If only you knew how much I think of you英语怎么回答带翻译 If only you knew how much I think of you 中文意思 If I knew how to abandon you ,that should have much good丶 什么意思? 英语翻译if only i knew how to operate an elecronic computer as you do 求翻译… If only I knew how to cook it! 跪求If They Only Knew-The 3Rd Storee歌曲链接 求类似If They Only Knew一样的歌这种节奏的好听的歌曲 We Keep quiet ’cause we’re dead if they knew 帮我翻译下 . if you knew what i knew歌词 If You Knew What I Knew 歌词 If You Knew What I Knew 歌词 years ago they knew many things about the moon.they knew how big it was and how far it was from the earth.中的it was 放在how big ,how far If I Knew Then 歌词