Answer:
[tex]\text{c) }\sqrt[4]{64}=2\sqrt[4]{4}[/tex]
Step-by-step explanation:
[tex]\text{a) }64\qquad\text{an integer; not a surd}\\\\\text{b) }\sqrt[6]{64}=2\qquad\text{an integer; not a surd}\\\\\text{c) }\sqrt[4]{64}=2\sqrt[4]{4}\qquad\textbf{a surd}\\\\\text{d) }\sqrt[3]{64}=4\qquad\text{an integer; not a surd}[/tex]