What can i say instead of "I think"

You could say "In my opinion..." or "I believe..."

Explanation:

As said by the first comment.

harlem's  cotton club boasted the talents of duke ellington. singers such as bessie smith and billie holiday popularized blues and jazz vocals. jelly roll morton and louis armstrong drew huge audiences as white americans as well as african americans caught jazz fever.

what is this from, i cant tell what language he uses without the piece of literature