The angles α,β,γ of a triangle are in arithmetic progression. If sin20α, sin20β, and sin20γ are in arithmetic progression, how many different values can α take?<spanclass=′latex−bold′>(A)</span>1<spanclass=′latex−bold′>(B)</span>2<spanclass=′latex−bold′>(C)</span>3<spanclass=′latex−bold′>(D)</span>4<spanclass=′latex−bold′>(E)</span>None of the above