Answer:
a. ___
Explanation:
The use of articles depends on the noun(s) or adjectives or anything equivalent to that. And depending on the number as well as the first letter of the noun, an article can be used.
But in the given sentence, the blank is before "London" which is a proper noun. Normally, a proper noun uses "the" or when the noun is definite. But in the given sentence, we will not use any article.
This is because it is talking about a particular place, and "the" is used only for those places that are states, or unions, or republics.
Thus, the final sentence will be
<em>"There are special hostels for the homeless in London."</em>
