Sentence Correction

Here is a question:

The magnitude of yesterday's earthquake has been determined by seismologists, but what really intrigues government officials are how to both detect warning singns of an earthquake and predict its location of impact.

My question is the following :

The right answer is :

has been determined by seismologists, but what really intrigues government officials is

This is what I said when I took the exam I don't know what is the rule to figure out the right answer?

Could you help me on that?

Thanks!

jimmy wrote:Here is a question:

The magnitude of yesterday's earthquake has been determined by seismologists, but what really intrigues government officials are how to both detect warning singns of an earthquake and predict its location of impact.

...has been determined by seismologists, but what really intrigues (you missed-it s addressing singular) government officials is

i hope this clarifies

it should be is . But i dont know for what reason ?

Are u saying intrigues is singular ?

aim-wsc wrote:

jimmy wrote:Here is a question:

The magnitude of yesterday's earthquake has been determined by seismologists, but what really intrigues government officials are how to both detect warning singns of an earthquake and predict its location of impact.

...has been determined by seismologists, but what really intrigues (you missed-it s addressing singular) government officials is

i hope this clarifies