30. The description set off by dashes in the highlighted phrase is meant to illustrate:

Answer and Explanation

Your Answer is

Correct Answer is G

Explanation

Item G: "description set off by dashes" in the title stem means that the content in the double quotation marks "face down, eyes closed, air out, reach, face up, eyes open, air in, reach" these contents express The author is learning to breathe for swimming.

Item F: Because it is practiced in the sea.

Item H: Because the description within the dash is just a breathing exercise, there is no stroke.

Item J: Many students are easy to choose by mistake. The content in the double dashes only describes the author's practice and does not indicate that the author was tricked by the grandmother into thinking that the grandmother could swim.