Final answer:
According to Chargaff's rule, if the DNA of a species contains 17% thymine, it will also contain 17% adenine. Therefore, the percentage of cytosine will be 17%.
Step-by-step explanation:
According to Chargaff's rule, the percentage of thymine (T) in DNA is always equal to the percentage of adenine (A), and the percentage of cytosine (C) is always equal to the percentage of guanine (G). Therefore, if the DNA of a species contains 17% thymine (T), it will also contain 17% adenine (A). Since the total percentage of thymine (T) and adenine (A) is 34%, the percentage of cytosine (C) and guanine (G) combined will also be 34%. This means that the DNA will contain 17% cytosine (C).