are (because texts are plural)

thank you @Vmusic ! thank you for your turther detailed answer!^^

Elizabeth is correct.... the tricky part comes in identifying the subject. Here it is "the texts" .... so since texts is plural, and you know this because of the 's', the correct verb here should be "are". The tricky part is identifying the subject by itself, and to put away the extra information about the subject, like Book 2 or Book 3. :-)

thank you @Elizabeth:)you are helpful!

Since the word 'texts' is more than one, it is 'are'. Example, The text of book 3 is more difficult than those of book 2 The texts of book 3 are more difficult than those of book 2 Good question! It is still hard for me to know, too!