Read an original passage from Mark Twain, and then read a student's excerpt from an essay about it. Is the student's excerpt written correctly?
A. Now when I had mastered the language of this water and had come to know every trifling feature that bordered the great river as familiarly as I knew the letters of the
alphabet, I had made a valuable acquisition.
B. Twain in his later years said that "when [he] had mastered the language of this water...[he] had made a valuable acquisition.

Your use of an ellipsis and brackets is correct, but "in his later years" should be in brackets.

The parentheses and ellipses are correct, but the bracket usage is incorrect.

Your use of ellipses, parentheses, and brackets is correct.

Your use of brackets is correct, but your ellipsis should have four dots.