Given the table of values of a Cosine Function, you know that the interval is:
[tex]\lbrack0,\pi\rbrack[/tex]By definition:
[tex]-1\leq cos(x)\leq1[/tex]By definition, the Period of the Cosine Function is the distance between the peaks.
Therefore, having:
[tex](0,1),(\pi,1)[/tex]You get that the Period is:
[tex]Period=\pi-0=\pi[/tex]Hence, the answer is: Third option.