1. A plane cuts a regular tetrahedron into two geometric bodies of the same shape and size. The number of such planes is
A. 3
B. 6
C. 10
D. Infinitely many
1. D Take the midpoints of a pair of opposite edges $AB, CD$ of the regular tetrahedron $ABCD$ as $E, F$ respectively, and draw any section through $E, F$ intersecting $BC, AD$ at $G, H$. According to the symmetry of the regular tetrahedron, the geometric bodies $AC-EGFH$ and $BD-EGFH$ have the same shape and size, so there are infinitely many planes that satisfy the condition.