Final answer:
The correct verb form to complete the sentence is 'puedan'.
Step-by-step explanation:
The correct verb form to complete the sentence is puedan. In this sentence, the subject is 'las comunidades indígenas' (the indigenous communities), which is a plural noun. Therefore, we need to use the third person plural form of the verb 'poder' (to be able to), which is 'puedan'. This verb form agrees with the subject and completes the sentence: 'Es indispensable que las comunidades indígenas puedan tener sus tierras' (It is essential that the indigenous communities can have their lands).
Learn more about Spanish verb conjugation