Step 1: Understand horizontal communication.
Horizontal communication occurs between individuals or groups at the same level in an organization. It is often used to share information, solve problems, or make decisions.
Step 2: Evaluate the options.
- Upward communication is from lower levels to higher levels of management.
- Downward communication flows from higher to lower levels of management.
- Parallel communication flows between colleagues or teams at the same level and is the correct answer.
Step 3: Conclude.
In horizontal communication, suggestions typically flow at the same level among peers or colleagues.
Final Answer:
\[
\boxed{\text{At parallel}}
\]