l could use a drink now.这里用could 有什么言下之意?为什么不直接说

有个英语句子请看I could really use a drink right now.我现在什么想喝水 可是在这个句 i could use a Could l （）use your car? you could give him a ticket to a ball game.这里为什么用to,作什么用? we could have had it all为什么不直接用have it all? Could i use your mobile and make a call?Certainly you ←这里填 c 这里为什么用could呢?You can buy as much as spaghetti as you could. He asked me whether I could help him.这里为什么用could could you tell me your name这里为什么要用could? could you come with me,please?这里为什么用could 而不用can 呢? 过去式I wish I could fly.这里为什么要用could?不用can? could use your car?