Answer to 3.5.1

A) A goes with D and B goes with C

B) The atom spacing is one half of the lattice constant

C) In B there are short stretches of alternating ...high/low/high...peaks while in A there are very few such alternating runs. B is the more ordered of the two. The weak "superlattice peaks" are stronger in C than in D: C corresponds to the more ordered structure.