Passive sentence (The number of automobiles ... greatly increased)

[Hiko]

I was wondering if someone could help me out with this one. The problem is like this. Which is grammatically correct?

1) The number of automobiles ______ greatly increased.

a. have
b. has
c. is
d. are

I argued that both b. and c. are correct. b. would be the more natural of the two, but c. is still valid as a passive sentence. The other person is saying that c. doesn't make any sense, and isn't grammatical. Please help.

Hiko

[Pamela]

"c" is more reasonable.

[Yankee]

Hi Hiko

For the sake of argument (or for the sake of winning an argument ), c. is theoretically possible, but in my opinion an appropriate context would be rare.

I think the best way for you to win your argument would be to come up with an appropriate context.

Amy

PS
I'd be interested in reading what you come up with.

[Lost_Soul]

Hi, Amy

I just incidentally ran into this discussion and it intrigued me a bit ...

So, what is the right answer ?

I personally would go for b The number of automobiles has greatly increased

[Yankee]

I agree with you, Alex.

As you can see, I'm still waiting for Hiko's further context.
.

[Lost_Soul]

Hi, Amy

I think he (or she) gave up on making up his context So much time has passed ever since

[Yankee]

Here's my try at a possible justification for (c):

Q: What happens whenever additional lanes are added to a highway?
A: The number of automobiles (that can and do use the highway) is greatly increased.
.

[Lost_Soul]

Hi, Amy

Sorry for my perseverance, but if I want to justify the b option, will this dialogue do the trick:

Q: What has happened to the number of cars on roads
A: It has greatly increased

or

Q: What happened to the number of cars on roads on some random date
A: It greatly increased then

Thank you !

[Yankee]

Hi Alex

It wasn't the tense that was the main problem, it was the voice. I think it would be most common to use the active voice (like both of your examples).

Option (c) is the present simple in the passive voice (I don't think you can look at the word 'increased' as an adjective in the sentence), so I tried to think up a context in which the number might be seen as increased by something.
.

[Lost_Soul]

Hi, Amy

Yeah, I see your point, thanks a lot !