gwd-1 25 ,math

gwd-1 25

If the sequence x₁, x_2, x_{3, …,} x_n, … is such that x₁ = 3 and x_n+1 = 2x_n – 1 for n ≥ 1, then x₂₀ – x₁₉ =

A.     2¹⁹

B.     2²⁰

C.     2²¹

D.     2²⁰ – 1

E.      2²¹ – 1

能不能详细解释一下！