Dr. Philip, along with his four distinguished colleagues, are presenti

I would say D. I don't think it is "is" because he isn't presenting "their" presentation rather they are presenting "Their" presentation.
Would make the most sense imo

But as well is additive phrase, which takes singular verb.

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According to official answer the correct sentence is B.
(B) Dr. Philip, along with his four distinguished colleagues, is presenting their dynamic theory of neuron regeneration at symposiums in Athens.


Here, we have background like:
Let's say that Dr. Philip is presenting dynamic theory neuron of regeneration at symposiums in Athens, and Dr. Philip and four distinguished colleagues are standing on a dais.

Here is the sentence for this background:
On the dais are four distinguished colleagues and Dr. Philip, who is presenting his dynamic theory of neuron regeneration at symposiums in Athens.
---> this sentence is not OK, because "who" indicates both Dr. Philip and four distinguished colleagues ( "Dr. Philip and four distinguished colleagues" treated as ONE word), but the ONLY 'doer' in this sentence is Dr. Philip.
So we can have some possible fixes on this issue who (Original issue):

On the dais are four distinguished colleagues and Dr. Philip, who is presenting his dynamic theory of neuron regeneration at symposiums in Athens.

1/
On the dais with four distinguished colleagues is Dr. Philip, who is presenting his dynamic theory of neuron regeneration at symposiums in Athens.

2/
On the dais are Dr. Philip, who is presenting his dynamic theory of neuron regeneration at symposiums in Athens, and four distinguished colleagues.
--> Here the subject is Dr. Philip and four distinguished colleagues.

3/
On the dais is four distinguished colleagues, along with Dr. Philip, who is presenting his dynamic theory of neuron regeneration at symposiums in Athens.
--> Here the subject is four distinguished colleagues.
4/
On the dais are four distinguished colleagues and Dr. Philip, the latter of whom is presenting his dynamic theory of neuron regeneration at symposiums in Athens.

We can make the number 3/ as creative as follows:
3/
Dr. Philip, along with four distinguished colleagues, is presenting his dynamic theory of neuron regeneration at symposiums in Athens.
--> Here the subject is Dr. Philip. along with four distinguished colleagues is just a modifier
So, the use of their in non-underlined part does not make sense to me at all.
I think, expert can explain it very well.
I'm tagging some of my favorite experts here.
RonPurewal, MartyTargetTestPrep, jennpt, AjiteshArun, ccooley, DmitryFarber, VeritasKarishma, GMATNinja, egmat, generis.
Bunuel
I've a curiosity to know the source of this question. Could you reveal the source, please?

Dr. Philip, along with his four distinguished colleagues, are presenting their dynamic theory of neuron regeneration at symposiums in Athens.

As we have plural pronoun in the non-underline portion, we need plural subject. As for my, either option is correct..

(A) Dr. Philip, along with his four distinguished colleagues, are - singular subject, does not match with "their"
(B) Dr. Philip, along with his four distinguished colleagues, is - same error as (A)
(C) Dr. Philip, in addition to his four distinguished colleagues, are - same error as (A)
(D) Dr. Philip, as well as his four distinguished colleagues, are - same error as (A)
(E) Dr. Philip and his four distinguished colleagues is - first plural subject, but the option is wrong for different reason (because of "is")

The proper answer choice should state something like this: Dr. Philip and his four distinguished colleagues are presenting their dynamic theory of neuron regeneration at symposiums in Athens.

According to official answer the correct sentence is B.
(B) Dr. Philip, along with his four distinguished colleagues, is presenting their dynamic theory of neuron regeneration at symposiums in Athens.


Here, we have background like:
Let's say that Dr. Philip is presenting dynamic theory neuron of regeneration at symposiums in Athens, and Dr. Philip and four distinguished colleagues are standing on a dais.

Here is the sentence for this background:
On the dais are four distinguished colleagues and Dr. Philip, who is presenting his dynamic theory of neuron regeneration at symposiums in Athens.
---> this sentence is not OK, because "who" indicates both Dr. Philip and four distinguished colleagues ( "Dr. Philip and four distinguished colleagues" treated as ONE word), but the ONLY 'doer' in this sentence is Dr. Philip.
So we can have some possible fixes on this issue who (Original issue):

On the dais are four distinguished colleagues and Dr. Philip, who is presenting his dynamic theory of neuron regeneration at symposiums in Athens.

1/
On the dais with four distinguished colleagues is Dr. Philip, who is presenting his dynamic theory of neuron regeneration at symposiums in Athens.

2/
On the dais are Dr. Philip, who is presenting his dynamic theory of neuron regeneration at symposiums in Athens, and four distinguished colleagues.
--> Here the subject is Dr. Philip and four distinguished colleagues.

3/
On the dais is four distinguished colleagues, along with Dr. Philip, who is presenting his dynamic theory of neuron regeneration at symposiums in Athens.
--> Here the subject is four distinguished colleagues.
4/
On the dais are four distinguished colleagues and Dr. Philip, the latter of whom is presenting his dynamic theory of neuron regeneration at symposiums in Athens.

We can make the number 3/ as creative as follows:
3/
Dr. Philip, along with four distinguished colleagues, is presenting his dynamic theory of neuron regeneration at symposiums in Athens.
--> Here the subject is Dr. Philip. along with four distinguished colleagues is just a modifier
So, the use of their in non-underlined part does not make sense to me at all.
I think, expert can explain it very well.