source: You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version.
target: You may can a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version.
references: You may can a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. A passage of up to 25 words as front and back cover text is allowed. You may add up to five words as a Front-Cover Text. You can add up to 25 words as a Back-Cover Text. You can put up to five words for the Front-Cover Text, 25 words for the back-cover text, to the end of the list or cover texts in the changed version. You are allowed to add a passage of up to five words as a Front-Cover Text.  You are allowed to add a passage of up to 25 words as a Back-Cover Text.  Both passages are added to the end of the list of Cover Texts in the Modified Version. You may add up to five words as a Front-Cover Text, and up to 25 words as a Back-Cover text, to the list of Covered Texts in the Modified Version. You can use up to five words as a Front-Cover Text, and up to 25 as Back-Cover Text. In the Modified Version you may add 25 words to the front and back covers. You may add up to five words as Front-Cover Text and up to 25 words as Back-Cover Text to the end of the list of Cover Texts. You can add up to five words of text to the Front Cover. You can add up to 25 words of texts to the Back Cover. Add your text at the end of the list of Cover Texts in the Modified Version.