Interesting question. A and B are clearly the the last ones you will boil down to. How does one decide between A and B?

that signifies the start of a restrictive clause, a clause that helps identify the subject. Lets take an example,

The restaurant that is located on Arthur road, offers great food.

In this sentence, that is located on Arthur road helps us identify which restaurant is being talked about.

Along similar lines, the way A is coded, it seems to suggest that there are (potentially) many Londons, but the London we are talking about here is the one that afforded its playwrights only two theaters. This is clearly absurd.

As used in B ("In a London"), it signifies a characteristic of London (that it afforded its playwrights only two theaters).

p.s. If the sentence were used in a 'non-restrictive' sense as follows, it would have been a contender:

In London, which afforded its playwrights only two theaters, Aphna Behn, by 1687, had 17 of her plays staged in as many years.

Thanks,

Ashish

Faculty @ EducationAisle
www.EducationAisle.com