2. Given a regular tetrahedron $ABCD$ with edge length 2, the sum of the areas of the sections obtained by all planes equidistant from its four vertices is $(\quad)$.
(A) 4
(B) 3
(C) $\sqrt{3}$
(D) $3+\sqrt{3}$
(Tip: There are two types of cross-sections: (1) one side of the cross-section has 1 point, and the other side has 3 points, there are 4 such cross-sections; (2) each side of the cross-section has 2 points, there are 3 such cross-sections., Answer: (D).)