本文主要学习“一般现在时”（the present tense）和“现在进行时”（the present continuous tense）两种时态各自的应用场景和区别。
一、一般现在时
The present tense is the most commonly used tense, but also the most prone to wrong with one.
1，一般现在时表示当前（时间段）的行为习惯或经常性的行为模式（重复行为）或行为倾向（喜好）。
I eat lunch. （我有吃中饭的习惯）
He rides a bicycle to school. （他一般骑自行车上学，行为模式）
She love swimming. （她喜欢游泳，行为倾向）
2，一般现在时表示一种状态（身份）。
I am a teacher. He is a good boy.
3，凡是真理，自然现象，科学公理，都要用一般现在时。
The sun rises in the east.
The earth is round.
The moon is a satellite of the earth.
America is a large country.
The sun never sets at the North Pole in summer.
Tree leaves absorb CO2 .
The basic principle of computers is Boolean algebra
Two points define a line.
Three points define a plane.
Three of the basic colors are red, yellow and blue.
4，一般现在有时会伴随副词“usually”、“every day”等。
二、现在进行时
现在进行时表示现在（时间点）正在进行的一个动作，或者表示一个有限的时间段正在进行的动作，强调正在进行。
verb to be + present participle （现在分词）
Examples:
I am calling my father.
He is swimming now.
He is playing basketball.
They are all eating now.
He is walking in the woods now.
He is reading a detective novel.
Mr. Brown is driving to work.
Mrs. Brown is cooking.
It is raining now.
三、差异
区别一：现在进行时强调目前正在进行的动作，而一般现在时强调经常性或习惯性的动作。如：
I’m reading a story now. 我在看一个故事。(目前正在干的事情)
I read stories in my spare time. 我有空时看故事。(经常性的行为)
区别二：现在进行时强调现阶段一直在进行的动作，而一般现在时只表动作的重复，而不表示动作的持续。如：
What are you doing these days? 这几天你在干什么？
They are learning English in the summer holiday. 他们暑假在学英语。
They read English every day. 他们每天读英语。
They play volleyball every Sunday. 他们每周星期天都打排球。
区别三：表示短促动作的动词(如 jump, knock, beat, pick, skip等)的进行时，表示动作的重复。如：
The girls are jumping over there. 女孩子们在那边跳。
His heart is beating fast. 他的心脏跳得很快。
区别四：某些表示希望或想法的动词(如hope, wonder, want等)的进行时可以表示委婉客气。如：
I’m hoping that you will succeed. 我正在希望你成功呢(www.yygrammar.com)。
I’m wondering whether you can help us now. 我不知道你现在能否给我们帮一忙。