It is given that $\triangle FED \sim \triangle STU$. Is it true to say that $\frac{DE}{ST} = \frac{EF}{TU}$? Why?

(B) No,it is not true.
Given that $\triangle FED \sim \triangle STU$,the corresponding vertices are $F \leftrightarrow S$,$E \leftrightarrow T$,and $D \leftrightarrow U$.
According to the property of similar triangles,the ratios of their corresponding sides must be equal.
Therefore,the correct ratios are $\frac{FE}{ST} = \frac{ED}{TU} = \frac{FD}{SU}$.
Comparing this with the given expression $\frac{DE}{ST} = \frac{EF}{TU}$,we can see that it does not match the required correspondence of sides.