Step 1: Meaning of the phrase.
The phrase "at a snail's pace" refers to moving or happening very slowly, just like how a snail moves at a slow speed.
Step 2: Analysis of the options.
\begin{itemize}
\item Very intelligent refers to someone with high intellect.
\item Very alert refers to someone who is keenly aware of their surroundings.
\item Very slowly refers to a slow movement, which matches the phrase "at a snail's pace."
\item Very fast refers to quick movement, which is the opposite of the phrase.
\end{itemize}
Step 3: Conclusion.
Thus, the correct answer is (C) very slowly.
Final Answer: \[ \boxed{\text{Very slowly is the correct answer.}} \]
The CEO's sudden resignation threw the board into a tailspin.
What does the idiom "threw into a tailspin" mean?