The correct answer is D. All of the above.
A good brick earth should contain about 20% to 30% of alumina, about 50% to 60% of silica, and not more than 5% of lime.
Alumina is a type of clay that is essential for making bricks. It helps to bind the other ingredients together and gives the bricks their strength. Silica is another type of clay that is also important for making bricks. It helps to make the bricks durable and resistant to weathering. Lime is a mineral that can be found in some brick earths. It can cause the bricks to expand and crack when they are fired, so it is important to keep the amount of lime in the brick earth to a minimum.
In addition to the above, a good brick earth should also be free of organic matter, salts, and other impurities. Organic matter can cause the bricks to rot, while salts can cause them to effloresce (form a white powder on the surface). Impurities can weaken the bricks and make them more susceptible to cracking.
If you are considering using a particular type of brick earth to make bricks, it is important to have it tested by a qualified professional to ensure that it meets the necessary requirements.