多久；多长时间

• "借"在英文中有三个词，① 借入，即borrow,如：May I borrow some books from the library?② 借出，如：I can lend my bike to you.③ 借多久要用keep, 因为borrow与lend都是截止性动词，而keep是延续性动词。如 How long can I keep it?
  
  ［误］ How long can I borrow this book?
  
  ［正］ How long can I keep this book?
  
  ［析］ "借"在英文中有三个词，① 借入，即borrow,如：May I borrow some books from the library?② 借出，如：I can lend my bike to you.③ 借多久要用keep, 因为borrow与lend都是截止性动词，而keep是延续性动词。如 How long can I keep it?

how soon/how long/how often

He sent another official to find out how soon the cloth would be ready.他又派了一位官员去看看还要多久布料才能织好。
He asked the doctor how long it had taken him to finish the operation.他问医生动这个手术花了多长时间？
How often does your father let you watch TV?你爸爸让你多久看一次电视？
<辨析>how soon 用来提问别人要“多快”能做好某事，所提问的部分一般是“要过多久以后”或“即刻”等意义的时间状语(如 in two weeks,before long,after March,at once 等)，多用于含将来意义的句子中。how long 用来提问“多长时间”，所提问的部分一般是“一段时间”的时间状语(如 for three days,since last week 等)。how often 意为“是否经常”、“多长时间一次”，所提问的部分一般是表示频度的副词或词组(如 sometimes.seldom,every day,once a week 等)。