fix some grammar errors on guide doc.

guides/source/active_record_querying.md

@@ -1219,7 +1219,7 @@ clients.each do |client|
 end
 ```
 
-This code looks fine at the first sight. But the problem lies within the total number of queries executed. The above code executes 1 (to find 10 clients) + 10 (one per each client to load the address) = **11** queries in total.
+This code looks fine at first sight. But the problem lies within the total number of queries executed. The above code executes 1 (to find 10 clients) + 10 (one per each client to load the address) = **11** queries in total.
 
 **Solution to N + 1 queries problem**
 
@@ -1453,7 +1453,7 @@ User.active.inactive
 # SELECT "users".* FROM "users" WHERE "users"."state" = 'active' AND "users"."state" = 'inactive'
 ```
 
-We can mix and match `scope` and `where` conditions and the final sql
+We can mix and match `scope` and `where` conditions and the final SQL
 will have all conditions joined with `AND`.
 
 ```ruby
@@ -1750,7 +1750,7 @@ Client.connection.select_all("SELECT first_name, created_at FROM clients WHERE i
 
 ### `pluck`
 
-`pluck` can be used to query single or multiple columns from the underlying table of a model. It accepts a list of column names as argument and returns an array of values of the specified columns with the corresponding data type.
+`pluck` can be used to query single or multiple columns from the underlying table of a model. It accepts a list of column names as an argument and returns an array of values of the specified columns with the corresponding data type.
 
 ```ruby
 Client.where(active: true).pluck(:id)

guides/source/active_record_validations.md

@@ -64,7 +64,7 @@ controller-level validations. Here's a summary of the pros and cons:
 * Controller-level validations can be tempting to use, but often become
   unwieldy and difficult to test and maintain. Whenever possible, it's a good
   idea to keep your controllers skinny, as it will make your application a
-  pleasure to work with in the long run.
+  pleasure to work within the long run.
 
 Choose these in certain, specific cases. It's the opinion of the Rails team
 that model-level validations are the most appropriate in most circumstances.

guides/source/autoloading_and_reloading_constants.md

@@ -171,7 +171,7 @@ Similarly, in the Rails console, if you have a user instance and reload:
 > reload!
 ```
 
-the `user` object is instance of a stale class object. Ruby gives you a new class if you evaluate `User` again, but does not update the class `user` is instance of.
+the `user` object is an instance of a stale class object. Ruby gives you a new class if you evaluate `User` again, but does not update the class `user` is an instance of.
 
 Another use case of this gotcha is subclassing reloadable classes in a place that is not reloaded: