Which of these is a natural wood defect rather than a result of improper storage and conditioning?
a) knot
b) warp
c) split
d) stain

Knot is a natural wood defect. The correct answer is A. Knot is a common type of natural defect in wood. There are four basic types of knots base on the size of their diameters, they are  pin, small, medium and large knots. The one with the highest diameter is the large knot while the pin knot has the smallest diameter. Knots tarnish the appearance of woods and reduce their strength.