Final answer:
The correct answer is 'which'. In this context, 'which' is a relative pronoun that links the two parts of the sentence and provides more information about 'Prague'.
Step-by-step explanation:
In the sentence you provided, the best choice to fill in the blank is 'which'. Thus, the sentence should read: 'I sometimes visit my grandmother in Prague, which is quite close to my home.' The word 'which' is a relative pronoun used to link the two parts of your sentence together. It refers back to 'Prague', giving us more information about that city. Use of 'which' ensures the sentence maintains proper English grammar.
Answer: I sometimes visit my grandmother in Prague, which is quite close to my home
Learn more about Relative Pronouns