======================
be的一般现在时形式
======================

+----------+---------+-------------+-------------+
| 肯定句   | 简略式  | 否定简略式  | 否定简略式2 |
+----------+---------+-------------+-------------+
| I am     | I'm     | I'm not     |             |
+----------+---------+-------------+-------------+
| You are  | You're  | You're not  | You aren't  |
+----------+---------+-------------+-------------+
| He is    | He's    | He's not    | He isn't    |
+----------+---------+-------------+-------------+
| She is   | She's   | She's not   | She isn't   |
+----------+---------+-------------+-------------+
| It is    | It's    | It's not    | It isn't    |
+----------+---------+-------------+-------------+
| We are   | We're   | We're not   | We aren't   |
+----------+---------+-------------+-------------+
| You are  | You're  | You're not  | You aren't  |
+----------+---------+-------------+-------------+
| They are | They're | They're not | They aren't |
+----------+---------+-------------+-------------+