Which of the following axis system is being satisfied by rhombohedral (trigonal) crystal system?

• A. a = b = c, α = β = γ = 90o
• B. a ≠ b = c, α = β = γ = 90o
• C. a = b ≠ c, α = β = γ = 90o
• D. a = b = c, α = β = γ ≠ 90o