What is the difference between like and as? On the GMAT test, like always means similar to. For example, if we say:

Like many other classical composers, Beethoven...

We mean to say that Beethoven is similar to many other classical composers.

Similarly, we might say:

There are so many sick people at this hotel that it's like a hospital (similar to).

However, if we say:

During the war, this hotel was used as a hospital.

Then we do not mean that the hotel was similar to a hospital. It really was a hospital, with doctors, patients, ambulances, etc. Unlike like, as often means identical. For example, if we say:

John is as tall as Marcos.

With that in mind, let us look at the sentence in question. Do we mean to say that cooperative apartment houses are similar to businesses or do we mean to say that cooperative apartment houses are businesses?

Answer choice (D) suggests that they are similar to businesses in some way, but are not actually businesses. This is why answer choice (D) is not the correct answer.

Hello!

The reason why option D is incorrect has to do with something called "nonessential clauses."

By putting the phrase "as dwellings" in between commas, we're telling the reader that information is non-essential to the meaning of the sentence. It basically means you could take it out without changing the core meaning. Let's look at what happens if we do this:

Answer D if it were written out completely:
Cooperative apartment houses have the peculiar distinction that, as dwellings, they must also operate like businesses.

Answer D if we took out the "nonessential" clause:
Cooperative apartment houses have the peculiar distinction that they must also operate like businesses.

By taking out the phrase "as dwellings," we now don't know what two things the apartment houses are supposed to be: a business and a what?? Therefore, we need to keep the part about them being dwellings for the sentence to truly make sense, making D incorrect.

I hope this helps! I'm available if you'd like any follow up.