However/though

Hello,

I'm going through some UoE practice tests for the CPE exam. For the part where I am to complete a gapped text, the key often includes more than one answer (sometimes there are more possible) so I know that most other anwers I may possibly come up with stand a good chance of being at least clumsy, if not clearly incorrect.

However, for the gap in the text below, the key lists HOWEVER as the only possible answer. I think THOUGH is also fine (that was what sprang to mind), but I suspect there might be a reason why it's not there?

Thanks for any answer

Lenka

Here is the text:

Five miles south-west of Lincoln lies Doddington Hall, a superb Elizabethan mansion with its historically-important walled gardens. Like most of the gardens around stately homes and period country houses, those at Doddington Hall reflect changing fashions in landscaping and planting ideas over the centuries.

What makes Doddington unusual, ________ , is that the gardens are still recognisably the same in structure as when they were laid out in the early part of the 17th century.