diff --git a/src/sec3.src.md b/src/sec3.src.md
index 1a2a4c2..d903549 100644
--- a/src/sec3.src.md
+++ b/src/sec3.src.md
@@ -42,7 +42,7 @@ The string `pr1.c` is the filename of the C source code above.
 $ gcc `pkg-config --cflags gtk4` pr1.c `pkg-config --libs gtk4`
 ~~~
 
-The C compiler gcc generates an executable file `a.out`.
+The C compiler gcc generates an executable file, `a.out`.
 Let's run it.
 
 ~~~
@@ -54,34 +54,38 @@ It should do one of these.
 $
 ~~~
 
-Oh, just an error message.
-But this error message means that the GtkApplication object ran without a doubt.
-Now, think about the message in the next subsection.
+Oh, it just produces an error message.
+This error message means that the GtkApplication object ran, without a doubt.
+Now, let's think about what this message means.
 
 ### signal
 
 The message tells us that:
 
-1. The application GtkApplication doesn't implement `g_application_activate()`.
-2. And it has no handlers connected to the "activate" signal.
-3. You need to solve at least one of these.
+1. The application GtkApplication doesn't implement `g_application_activate()`,
+2. It has no handlers connected to the "activate" signal, and
+3. You will need to solve at least one of these.
 
 These two causes of the error are related to signals.
-So, I will explain it to you first.
+So, I will explain that to you first.
 
-Signal is emitted when something happens.
+A signal is emitted when something happens.
 For example, a window is created, a window is destroyed and so on.
-The signal "activate" is emitted when the application is activated.
-If the signal is connected to a function, which is called signal handler or simply handler, then the function is invoked when the signal emits.
+The signal "activate" is emitted when the application is activated, or started.
+If the signal is connected to a function, which is called a signal handler or
+simply handler, then the function is invoked when the signal emits.
+
 The flow is like this:
 
 1. Something happens.
 2. If it's related to a certain signal, then the signal is emitted.
-3. If the signal is connected to a handler in advance, then the handler is invoked.
+3. If the signal as been connected to a handler, then the handler is invoked.
 
 Signals are defined in objects.
-For example, "activate" signal belongs to GApplication object, which is a parent object of GtkApplication object.
-GApplication object is a child object of GObject object.
+For example, the "activate" signal belongs to the GApplication object, which is
+a parent object of GtkApplication object.
+
+The GApplication object is a child object of the GObject object.
 GObject is the top object in the hierarchy of all the objects.
 
 ~~~
@@ -90,7 +94,7 @@ GObject -- GApplication -- GtkApplication
 ~~~
 
 A child object inherits signals, functions, properties and so on from its parent object.
-So, Gtkapplication also has the "activate" signal.
+So, GtkApplication also has the "activate" signal.
 
 Now we can solve the problem in `pr1.c`.
 We need to connect the "activate" signal to a handler.