This passage is designed to a) explain why the great blue hole formed. b) describe what the great blue hole is like. c) encourage the reader to study other blue holes. d) persuade the reader to visit the great blue hole.

the words "slavery," "devils," and "murderer" evoke a sense of disgust.

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.)