Answer:
Credential is the word which you require.
The difference between free verse and black verse is free verse has no rhythm. Free verse flows naturally, I guess you can say. It doesn't rhyme. It's kinda like as song. Most songs don't rhyme unless it's rap. So, songs are categorized as free verse while rap is categorized as, well, a rhyme that rhymes.
Commodore Perry of the US forced Japan to trade, which led to Japan opening its ports to more trade. MacGregor comments that this time signaled a shift toward greater economic power for Japan.
