One interval is given in interval notation, another in set-builder notation. Match the equivalent intervals.

1. (-∞, ∞)
2. (-∞, 3)
3. [3, ∞)
4. (3, ∞)

a. {x l 3 ≤ x < ∞
b. {x l x ∈ ℝ}
c. {x l -∞ < x < 3}
d. {x l 3 < x < ∞}