The correct answer is A. Parallel to grains.
Timber is strongest in the direction parallel to the grain. This is because the fibers in the wood are aligned in this direction, and they provide the most resistance to force. When a force is applied parallel to the grain, the fibers are able to slide past each other, which helps to distribute the force and prevent the wood from breaking.
When a force is applied perpendicular to the grain, the fibers are not able to slide past each other as easily. This puts more stress on the wood, and it is more likely to break.
A force applied at a 45° angle to the grain will cause some of the fibers to be stressed in tension and some to be stressed in compression. This can cause the wood to split or crack.
Therefore, the strength of timber is maximum in the direction parallel to the grain.