An insect moves at a speed of 3 20 feet per second. What is this speed,

Choice A is correct. It’s given that $3 \text{feet}=1 \text{yard}$. It follows that a speed of $\frac{3}{20}$ feet per second is equivalent to $\left(\frac{{\displaystyle \frac{3}{20}} \text{feet}}{1 \text{second}}\right)\left(\frac{1 \text{yard}}{3 \text{feet}}\right)$, which is equivalent to $\left(\frac{3}{20}\right)\left(\frac{1}{3}\right)$, or $\frac{1}{20}$, yards per second.

Choice B is incorrect. This is the speed, in feet per second, that's equivalent to $\frac{3}{20}$ yards per second.

Choice C is incorrect. This is the speed, in yards per second, that's equivalent to $18$, not $\frac{3}{20}$, feet per second.

Choice D is incorrect. This is the speed, in yards per second, that's equivalent to $60$, not $\frac{3}{20}$, feet per second.