Answer: A.
Explanation:
Two independent clauses can be connected by using a comma followed by a coordinating conjunction like the ones below:
for
and
nor
but
or
yet
so
The best correction of the sentence would be:
We ran to catch up with the bus, but we missed it by just a few seconds.
The characteristics of a simple subjects is that is has a subject and a verb.
The answer is A inability to act