1 = H in a D ---> 1 = Holes in a Donut
There is no specific catergory, the answers range from famous sayings to geography to science and so on.
1 = M L on the C F = Maple Leaf on the Canadian Flag
1 = R A in a E B = Rotten Apple in Every Bunch/Bushel
1 = W on a U = Wheel on a Unicycle
2 = G of V = Gentlemen of Verona
2 = P in a P = Peas in a Pod
3 = B M (S H T R) = Blind Mice (See How They Run)
3 = L K that L T M = Little Kittens that Lost Their Mittens
3 = P into which A G was D = Provinces into which Ancient Gaul was Divided
3 = S Y O at the O B G = Strikes You're Out at the Old Ball Game
3 = V in a T = Vertices in a Triangle
3 = W on a T = Wheels on a Tricycle
4 = Q in a G = Quarts in a Gallon
4 = S in a Y = Seasons in a Year
4 = S on a V = Strings on a Violin
5 = D in a Z C = Digits in a Zip Code
5 = F on a H = Fingers on a Hand
5 = T on a F = Toes on a Foot
5 = T on a C (including the S in the T) = Tires on a C (including the Spare in the Trunk)
6 = B to an O in C = Balls to an Over in Cricket
6 = C in a P C = Characters in a Postal Code - Canada
6 = L and N in a P C = Letters and Numbers in a Postal Code - Canada
6 = P on a B T = Pockets on a Billiard Table
6 = P on a P T = Pockets on a Pool Table
6 = W of H the E = Wives of Henry the Eighth
7 = B for S B = Brides for Seven Brothers
7 = C on the W = Continents on the World
7 = D in a W = Days in a Week
7 = D with S W = Dwarves with Snow White
7 = W of the A W = Wonders of the Ancient World
7 = Y of B L for B a M = Years of Bad Luck for Breaking a Mirror
8 = D a W (in the B S) = Days a Week (in the Beetles' Song)
8 = P of S in the E L = Parts of Speech in the English Language
8 = S on a S S = Sides on a Stop Sign
8 = T on an O = Tentacles on an Octupus
9 = J on the S C = Justices on the Supreme Court
9 = L of a C = Lives of a Cat
9 = P in S A = Provinces in South America
9 = P in the S S = Planets in the Solar System
9 = P on a B T = Players on a Baseball Team
10 = C = Commandments
10 = D in a T N (including the A C) = Digits in a Telephone Number (including the Area Code)
10 = L I = Little Indians
11 = P in a F (or S) T = Players in a Football (or Soccer) Team
12 = D of C = Days of Christmas or Disciples of Christ
12 - 20000