Explanation:

Correct Answer is (a).Over 17 million Brits come to Spain every year and many of them live here or retire here and we want to keep it that way as much as possible. This is correct.
It would have made me much more adventurous and experimenting by then even though and we want to keep it that way as much as possible.
This is meaningless and incorrect.
How much longer do we continue to complain about the lack of a headphone jack before we realize it's a lost cause and we want to keep it that way as much as possible.
This is correct in terms of grammar but illogical. If we complain about something, why would we want to keep it that way as much as possible.
Hence, option A is correct.