A four-digit pin number is needed to access a bank account. How many different four-digit pin numbers are possible if no number can be used twice, and the first and third digits must be odd, and the second and fourth digits must be even?
Given more time, we could done the work better. ……. 如果提供更多的时间，我们会做得更好。
|I’ll go out tomorrow||unless||
|I’ll go out tomorrow||even if||
|（主语 + 谓语+ 状语）||引导词||（主语 + 谓语）|
it rains 已是“主谓”结构的语句，通过引导词作引导成为状语从句来修饰 “I’ll go out tomorrow”，引导词不同，整个句子表达的意思也就不一样
条件、让步状语从句由从属连词 if、 unless ( = if not ) 、 as long as ( = so long as ) 引导
unless ( = if not ) ：除非，如果不
as long as ( = so long as ) ：只要
If I were you, I would go to see Mr.Lee at once. …………… 如果我是你，我会马上去找李先生的。
I’ll go out tomorrow unless it rains. = I’ll go out tomorrow if it dose not rain.
I wouldn’t give up unless he give up first. = I wouldn’t give up if he doesn’t give up first.
As long as you drive carefully, you will be very safe. …………… 只要你小心驾车，你会很安全的。
There is hope so long as he is with us. . …………… 只要他在就有希望。
让步状语从句可由 though ( = although) 、 as、 even if ( = even though ) 、 whether … or not 、 no matter ( what、 who、 when、 which、 where、 how )
1. though = although：虽然。 一般 although 只用在句首，而 though 可用在句中任何位置，他们都不能够与 but 连用
He knows much though he is young.
He is young, but he knows much.
Althought ( Though )he is young, but he knows much. …………… （×）
even if ( = even though ) ： 尽管，即使
whether … or ( not )：不管怎样，无论如何；
不论 … 还是 …
Tired as he was, he sat up late. …………… 他虽然疲倦，可仍然熬夜到很晚才睡。
I’ll go out tomorrow even if it rains. …………… 即使明天下雨，我还是外出。
Even though he tried, he still lagged behind other runners.
I’ll go out tomorrow whether or no it rains. …………… 无论是否下雨，我明天将会外出。
Whether they go or stay, it makes no odds. …………… 他们是去是留都没多大关系。
3. no matter ( what、 who、 when、 which、 where、 how ) ：不论 ( 什么、谁、什么时候、哪一个、什么地方、如何) ，可以由 ~ever 构成的合成词替代
No matter who break the law, he will be punished. = Whoever break the law, he will be punished.
No matter when you come, you’ll be welcome. = Whenever you come, you’ll be welcome.
No matter which they choose, we must accept their decision.
Whichever they choose, we must accept their decision.
No matter where she goes, there are crowds of people waiting to see her.
Wherever she goes, there are crowds of people waiting to see her.
No matter how hungry I am, I never seem to be able to finish off a whole pizza.
However hungry I am, I never seem to be able to finish off a whole pizza.
A right circular cylinder having a finite height with circular ends perpendicular to the axis as shown in the figure. If the ends are open, it is called an open cylinder. If the ends are closed by flat surfaces it is called a solid cylinder.
A closed, symmetric curve shaped like an oval, which can be formed by intersecting a cone with a plane that is not parallel or perpendicular to the cone’s base. The sum of the distances of any point on an ellipse from two fixed points (called the foci) remains constant no matter where the point is on the curve.