The correct answer is: A. Bed joint.
A bed joint is a mortar joint in masonry which is normal to the face of wall. It is the horizontal joint between two masonry units. The bed joint is the most important joint in masonry, as it is the joint that supports the weight of the wall. The bed joint must be strong and well-formed to ensure the stability of the wall.
A wall joint is a vertical joint between two masonry units. It is the joint that runs perpendicular to the face of the wall. The wall joint is not as important as the bed joint, as it does not support the weight of the wall. However, the wall joint must still be strong and well-formed to prevent water from entering the wall.
A cross joint is a diagonal joint between two masonry units. It is the joint that runs diagonally across the face of the wall. The cross joint is not as important as the bed joint or the wall joint, as it does not support the weight of the wall and does not prevent water from entering the wall. However, the cross joint should still be strong and well-formed to improve the appearance of the wall.
A bonded joint is a joint between two masonry units that is filled with mortar. The bonded joint is the strongest type of joint, as it provides a continuous bond between the masonry units. The bonded joint is the most common type of joint used in masonry construction.