The correct answer should be: "[...] only human language utilizes complex system of speech".
Explanation:
Although animals such as dolphins and great apes communicate, which is a form of language, only humans are capable of producing speech through the use of words and a complex set of phrases and sentences. Animals do not speak, even though they communicate differently, only people are able to use language in this way, only humans use a complex system of language data inside out their minds while using oral or written speech.
