TOEFL GRAMMAR: some + singular noun?

[holmes]

This sentence I’ve taken from Test Preparation Kit of ETS:

A mirage is an atmospheric optical illusion in what an observer sees a nonexistent body of water or an image of some object.

Of course , the answer is B in which. But this means D is correct . Object is uncounted noun??? If not, is this sentence wrong?

[Erin]

Great question!!

This is a very common mistake; a lot of people think that some must always be followed by a plural noun. This is not true--it is very easy to use a singular noun after some (as we see here).

And you know what? The funny thing is that we all already know this. Think about the words or phrases someday, someone, some year--they all have something in common.

Can you figure it out?

They all refer to a noun that is unidentified, i.e., a noun that we don't yet know about.

Here's a very common example:

Some guy called you while you were gone.

In this case we use some guy because we don't know who it is.

Hope that helps.

[holmes]

Great answer!!!
I GOT IT.
Thanks a lot , Erin.

[poli]

Hi,pals!
I just read the explanations about holmes`s question,but I didn`t get what word should be put instead ``object`?
Thank u!

[Erin]

No, "object" is correct as written. We need to change "in what" to "in which."

[meteor]

Thank a lot. I have undergone the answer now. I also understand other questions, for example:
Some friend kicked me while I was reading some books yesterday.

[kronique]

is it some friends???

[lindaenvir]

This sentence I’ve taken from Test Preparation Kit of ETS:

A mirage is an atmospheric optical illusion in what an observer sees a nonexistent body of water or an image of some object.

Of course , the answer is B in which. But this means D is correct . Object is uncounted noun? If not, is this sentence wrong?

SOME used with singular countable nouns to refer to a person, place, thing or time that is not known or not identified:
There must be some mistake. * He's in some kind of trouble. * She won a competition in some newspaper or other. * I'll see you again some time, I'm sure.
Right?