1. Have you ever seen the lights downtown during the holidays they are amazing.
b. run-on sentence
A run-on sentence is a sentence consisting of two or more independent clauses not separated by a period, semicolon or joined by a conjunction and that, instead, are connected with a comma (which it's wrong) or without any type of punctuation. The sentence provided has these characteristics, as for the second clause “they are amazing” should be separated from the first one with a question mark. The corrected version of the sentence is the following: Have you ever seen the lights downtown during the holidays? They are amazing.
2. Our neighborhood looks really pretty in the wintertime. When the snow is falling and everything is quiet.
a. sentence fragment
A sentence fragment is a group of words similar to a sentence in the sense that it starts with a capital letter and ends with and an end mark but that it is not a sentence because it does not convey a complete idea. In this sense, a sentence fragment is more like a phrase or a dependent clause, but standing alone. “When the snow is falling and everything is quiet” is an example of a sentence fragment (it is a dependent clause standing alone). We can fix it by connecting it to the previous sentence with a comma.
3. Dad doesn’t like winter, he hates shoveling snow.
b. run-on sentence
This is a run-on sentence because it is separated by a comma when it should be separated by a period or connected by coordinating conjunction like “and.”