Answer and Explanation:
If I am not mistaken, you want to determine which sentences are grammatically correct. Here are the ones that are correct and incorrect and the reasons why:
1. <em>Correct</em>
Because she waited until the last minute, she could not order gifts online.
Correct punctuation - a comma is correctly placed between the dependent and independent clauses.
2. <em>Incorrect</em>
It should be the first one:
Every year, to celebrate the holiday, I bake Christmas cookies with my grandmother.
<u>Why?</u>
A comma is necessary in this case between the dependent (<em>to celebrate the holiday</em>) and the independent clause (<em>I bake Christmas cookies</em>...) as the longer the sentence gets, the more confusing could be without any pauses - or commas -.
3. <em>Correct</em> (although it is not visible)
It should be:
Though it was 85 degrees last Christmas, I still wore a sweater.
First sentence is dependent (begins with a subordinating conjunction) and needs a comma to separate it from the independent clause.
4. <em>Incorrect - in many cases</em>
It should be:
We eat turkey, potatoes, and greens on Christmas Day.
<u>Why?</u>
Although this is a topic of debate, the serial comma serves to separate more than two objects or nouns and it is the most appropriate way to separate items.
5. <em>Correct</em>
In many countries, December 26 is known as Boxing Day.
First clause - in many countries - is a dependent clause (it needs the other clause to make sense), so it needs to be separated with a comma from the independent clause to avoid confusion.
