1、表示多長(zhǎng)時(shí)間，主要用來對(duì)一段時(shí)間(如three days, four weeks 等)提問,答語通常是（for）three days/weeks/months等時(shí)間段,它可用于各種時(shí)態(tài)。
It did not take us long to nail that lie.
沒多久我們就把謊言揭穿了。
He is sure to spill the beans before long.
用不了多久他準(zhǔn)會(huì)走漏消息的。
How long does it take to get to London from here? 從這里到倫敦要多長(zhǎng)時(shí)間?
At least ten hours. 至少要10個(gè)小時(shí)。
2、表示某東西有多長(zhǎng)。如：
How long is the river? 這條河有多長(zhǎng)？
About 500 km. 大約500千米。
How long is the tunnel? 隧道有多長(zhǎng)？
You sneak a look at your watch to see how long you've got to wait.