Which statement is incorrect?

• A
  $\alpha$-rays have more penetrating power than $\beta$-rays.
• B
  $\alpha$-rays have less penetrating power than $\gamma$-rays.
• C
  $\beta$-rays have less penetrating power than $\gamma$-rays.
• D
  $\beta$-rays have more penetrating power than $\alpha$-rays.