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Hi, I am trying create different forums for different Exams under one WordPress website using bbpress. I am bit confused about the Forum and Category. Let me know which on of the following is correct?

#1 ——————————————————

Forum 1 (eg. Exam 1)

Category 1 (eg. Math)
Topic 1

Category 2 (eg. English)
Topic 1

Category 3 (eg. Science)
Topic 1

Forum 2 (eg. Exam 2)

Category 1 (eg. Math)
Topic 1

Category 2 (eg. English)
Topic 1

Category 3 (eg. Science)
Topic 1

———————————————————

#2 ——————————————————

Forum 1 (eg. Exam 1)

Sub-forum 1
Category 1 (eg. Math)
Topic 1

Sub-forum 2
Category 2 (eg. English)
Topic 1

Sub-forum 2
Category 3 (eg. Science)
Topic 1

Forum 2 (eg. Exam 2)

Sub-forum 1
Category 1 (eg. Math)
Topic 1

Sub-forum 2
Category 2 (eg. English)
Topic 1

Sub-forum 2
Category 3 (eg. Science)
Topic 1
———————————————————

After creating the forums I want to create menu with dropdown list of Forum 1, Forum 2, etc.