first, firstly or at first

本文详细解释了英语中first和firstly的区别及其用法。first可用作形容词或副词,通常用于指时间、顺序上的第一;firstly则更正式,常用于列举条目。同时介绍了at first的含义及应用场景。

First and firstly

First can be an adjective or an adverb and refers to the person or thing that comes before all others in order, time, amount, quality or importance:

What’s the name of the first person who walked on the moon? (adjective)

Beth always arrives first at meetings. (adverb)

We often use first, especially in writing, to show the order of the points we want to make. When we are making lists, we can use first or firstly. Firstly is more formal than first:

Dear Mr Yates

First(ly) I would like to thank you for your kind offer of a job

Not: At first I would like to thank you

First(ly) the sodium chloride is dissolved in the water and heated gently. Second(ly) a dye is added to the solution.

Not: At first, the sodium chloride

At first

At first means ‘at the beginning’ or ‘in the beginning’ and we use it when we make contrasts:

At first when I went to England to study English, I was homesick, but in the end I cried when it was time to leave.

He called for help. No one heard him at first, but eventually two young girls came to help him.


用c++和segment tree解决下述问题Doing Exercises 描述 As we all know, the lines of students doing exercises between classes are always unsatisfactory to teachers. Today, a teacher wants to require something new. Firstly, he lets some students of N classes correspondingly form n lines. Then, he randomly selects a class to add some of its remaining students to its line, or selects a class to let some students leave its line, or lets the monitors from some adjacent classes report the total number of students in all these classes. This is very annoying for the monitors. Can you write a program to help them complete the reporting task? 输入 The first line is an integer T (T<50), the number of test cases. For each test case, its first line is an integer N (1<=N<=50000), representing the number of classes, and its second line include N integers (a1, a2, a3, ... , an), and ai (1<=ai<=100) means the number of students in the line of class i at the beginning. Then, each next line will be an order. There are 4 kinds of orders: (1) "Add x i" means adding x students to the line of class i; (2) "Sub x i" means that x students leave the line of class i; (3) "Query i j" means that the monitors from class i to class j report the teacher the total number (sum) of students in their classes at that moment (i<j); (4) "End" means ending the exercises, which will only appear at the end of each test case. The number of orders will not exceed 40000. The number of students in any line will never below 0. 输出 For each test case, you must print "Case i:" in the first line. Then for each Query, print the result in one line.
06-09
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