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. Correct
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. Incorrect
It should be the first one:
Every year, to celebrate the holiday, I bake Christmas cookies with my grandmother.
Why?
A comma is necessary in this case between the dependent (to celebrate the holiday) and the independent clause (I bake Christmas cookies...) as the longer the sentence gets, the more confusing could be without any pauses - or commas -.
3. Correct (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. Incorrect - in many cases
It should be:
We eat turkey, potatoes, and greens on Christmas Day.
Why?
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. Correct
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.