CHOOSE THE CORRECT OPTION :

It's is, whoever is saying are is wrong. You can easily see this by rearranging the sentence so it isn't interrupted by the non-essential clause about the magazines: The book is on the table along with the magazines. It doesn't make sense to say: The book are on the table along with the magazines. Now if the sentence said "the book and the magazines" then are would be used. The reason it's not here is the clause between the two commas is called a non-essential clause. It's basically a group of words added to a sentence between two commas that can be removed and the sentence will still function and the main point of the sentence will not change. It's added to give further context or additional information. In your example, the fact that magazines are on the table along with the book does not change the point of the sentence which is that the book is on the table. Example: John, who used to work with me, is now a local celebrity. In that case, "who used to work with me" is a non-essential clause.

Wow I feel dumb. The right answer is "is", but I got confused by the interupter and clicked "are". "Were" would also be perfectly acceptable in the right context, but "have been", is it not correct.

I put were because it's also right. 'is" would be present tense, "were" would be past. For people getting tripped up, remove "along with the magazines" and say the sentence. Sounds much better and adding it back shouldn't change "is" to "are".

intervening phrases (in between two commas) do not count towards your number of subjects.

The book, along with the magazines, ......... on the table. -> is 'Along with the magazines' is a prepositional phrase. You can take it out of the sentence, and the sentence will read as it should.

It's is, but I was about 0.0001 seconds away from submitting were.

I forgot how tricky English can be

While it is "is", I wouldn't think twice if I heard/said "are" in practice in daily speech.

“The book” is a singular noun, and only one of those options is singular. Otherwise, it could be any tense.

Is and were are both correct

The correct answer is “is.” However, this is a pretty awkward sentence and it’d be unusual for a native speaker to construct it this way. If you said this aloud, I don’t think anyone would blink twice if you said “are” instead of “is,” even if it’s technically incorrect.