The underlined verbal phrase "to take their tusks" is an infinitive. Infinitives are formed by "to" followed by the base form of a verb. In this case, "to take" is the infinitive form.
Identify the underlined verbal or verbal phrase as a gerund, a participle, or an infinitive.
Hunters kill the African elephants to take their tusks. With the underlined part being "to take their tusks"
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