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Control Flow
Boolean Expressions

In order to build control flow into our program, we want to be able to check if something is true or not. A boolean expression is a statement that can either be `True` or `False`.

Let’s go back to the ‘waking up’ example. The first question, “Is today a weekday?” can be written as a boolean expression:

``Today is a weekday.``

This expression can be `True` if today is Tuesday, or it can be `False` if today is Saturday. There are no other options.

Consider the phrase:

``Friday is the best day of the week.``

Is this a boolean expression?

No, this statement is an opinion and is not objectively `True` or `False`. Someone else might say that “Wednesday is the best weekday,” and their statement would be no less `True` or `False` than the one above.

How about the phrase:

``Sunday starts with the letter 'C'.``

Is this a boolean expression?

Yes! This expression can only be `True` or `False`, which makes it a boolean expression. Even though the statement itself is false (Sunday starts with the letter ‘C’), it is still a boolean expression.

### Instructions

1.

Determine if the following statements are boolean expressions or not. If they are, set the matching variable to the right to `"Yes"` and if not set the variable to `"No"`. Here’s an example of what to do:

Example statement:

``My dog is the cutest dog in the world.``

This is an opinion and not a boolean expression, so you would set `example_statement` to `"No"` in the editor to the right. Okay, now it’s your turn:

Statement one:

``Dogs are mammals.``

Statement two:

``My dog is named Pavel.``

Statement three:

``Dogs make the best pets.``

Statement four:

``Cats are female dogs.``