Use grep to find any lines with duplicate words on it.
Use sed to append to the end of the line a period.
Use sed to substitute the 2nd from last space (ASCII 32) on line with a -.
Use sed to substitute the 3nd from last space (ASCII 32) on line with a -.
Use sed to substitute the 1st space (ASCII 32) on line with a -.
Use sed to substitute the 2nd space (ASCII 32) on line with a -.
Use sed to substitute the 3nd space (ASCII 32) on line with a -.
Use sed to display only lines 7, 14, Use -n option and the p modifier. 
Use sed to display only lines 9, 22, Use -n option and the p modifier. 
Use sed to display only lines beginning with a capital word, Use -n option and the p modifier. 
Use sed to display only lines containing exactly 4 words.
Use sed to display only lines containing exactly 6 words.
Use sed to display only lines containing at least 3 words.
Use sed to display only lines containing at least 5 words.