The correct option is A how you are getting on
A clause is a part of a larger sentence containing a subject and a predicate of its own.
A Principal Clause is an independent clause which can exist even without a subordinate clause. A Subordinate Clause is called a dependent clause because it cannot exist without the help of the principal clause. It begins with a subordinating conjunction.
Option B is correct as 'how you are getting on' is the subordinate clause, beginning with the subordinating conjunction 'how'. It depends upon the principal clause for its existence.
Option C and Option D are incorrect as they do not make any sense.