Your teacher gave you an assignment to complete two weeks ago. It is
due today, and you have not completed the assignment. You tell your
teacher that your internet was down last night. Is your argument valid?
Why or why not? What would a better argument be? (Minimum 7-10
complete sentences)

No, your argument is not valid. It is not valid because if you would have done the assingnement sooner, you would have been able to get it done in time for said due date. Unless you have a valid excuse as to why you could not complete it sooner, that is. If you would have explained  to your tecaher sooner that your internet was down, maybe say the beginning of week two; that would have been a different story, and maybe you would have been allowed an extended time period to complete the assignment.

((I'm not sure if that's 7, but I couldn't drag it on any longer, hope this helps! <3)

Explanation:

Your argument isn't valid because you could've told her about it and be able  to complete in school. You could've also gone to the library to complete it. You could have written the answer down on paper to complete the assignment. Lastly, you said your internet was down last night. You've had two weeks to complete this assignment.  I don't think a better argument is possible. Teachers can spot a lie from a mile away.