Why was Bessie Coleman's struggle even more difficult than Harriet
Quimby's?

I think She had to struggle with racial prejudice and became the first African-American to earn a pilot's license. She was determined to get her pilot's licenses. She was smart and was the first woman in America to become a licensed pilot.

I Hope I answer it right. *_*

not concrete, existing in thought or as an idea but not having a physical or concrete existence

a. "to practice" is the best phrase to complete the sentence.

explanation:

during the summer, she likes to practice her soccer skills so that she is ready to play in the fall.

(note that : all the other options "the practicing of", "practice for" and "to do a practice on" are inappropriate as they make the sentence grammatically incorrect.)