The best revision to combine sentences two and
three is this one:
<span>
"Let freedom ring” is a phrase which is used many times in Dr.
Martin Luther King Jr’s speech that leads to an exciting conclusion.</span>
<span>
In order to construct correct compound sentences, you should omit words
that contribute to redundancy. </span>
<span>Secretariat was an American Thoroughbred racehorse who, in 1973, became the first Triple Crown winner in 25 years.
He died in 1970.
</span>
I think it’s b because it presents the actions
D(set in motion, cause to start