Select all of the true statements from the following,
a. f(x) ∈ O(g(x)) ⇒ g(x) ∈ Ω(f(x))
b. f(x) ∈ o(g(x)) ⇔ f(x) ∈ O(g(x))
c. f(x) ∈ O(g(x)) ⇒ f(x) ∈ θ(g(x))
d. f(x) ∈ o(g(x)) ⇒ f(x) ∈ O(g(x))
e. f(x) ∈ θ (g(x)) ⇒ f(x) ∈ O(g(x))