Which sentence does not contain any errors in comma usage?

a.
everything turned out for the best, after all.

b.
in fact los angeles does have a public transportation system.

c.
people's houses generally speaking, have roofs.

d.
the dam moreover, was only three years old.

c -invasion by the moroccans.

dr. kings dream speech

explanation:

it was late in the day and hot, and after a long march and an afternoon of speeches about federal legislation, unemployment and racial and social justice, the rev. dr. martin luther king jr. finally stepped to the lectern, in front of the lincoln memorial, to address the crowd of 250,000 gathered on the national mall.