Answer:
A. before the disease, but losing his vision
Step-by-step explanation:
The best way to rewrite the sentences is:
He had played sports before the disease, but losing his vision meant that ball games were out.
Option B is wrong because two independent clauses should be separated by a period mark or a semicolon, not a comma:
He had played sports before the disease, however, losing his vision meant that ball games were out.
Options C and D are wrong because there are no punctuation marks to organize the sentences:
He had played sports before the disease losing his vision meant that ball games were out.
He had played sports before the disease that losing his vision meant that ball games were out.