Whereas many animals such as dolphins and great apes, communicate with each other through gestures and sounds, only human language utilizes complex system of:

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.