你问别人, 我们什么时候出发呢? 要是别人说, "It's up to you.", 就是说你决定就可以啦! 要是更客气一点, 就是 "It's totally up to you.".  另外一个常常用到的回答方式就是, "It depends." 翻成中文就是视情况而定.  例如别人跟你说, "I need a place to stay." 你就可以答, "It depends how long are you gonna stay." 这需要视你待多久而定吧!