The correct answer is A. Mortise and tenon joint.
A mortise and tenon joint is a type of woodworking joint that is used to join two pieces of wood together. The joint consists of a mortise, which is a rectangular hole that is cut into one piece of wood, and a tenon, which is a rectangular piece of wood that fits into the mortise. The tenon is then glued and nailed or screwed into place, creating a strong and secure joint.
Mortise and tenon joints are commonly used in timber trusses, which are structures that are used to support roofs and other heavy loads. The joints are used to join the principal rafters and tie beams, which are the main structural members of the truss.
The other options are incorrect because they are not commonly used in timber trusses. A butt joint is a simple joint that is made by butting two pieces of wood together and then fastening them with nails or screws. A mitred joint is a joint that is made by cutting two pieces of wood at a 45-degree angle and then joining them together. An oblique mortise and tenon joint is a type of mortise and tenon joint that is made with a mortise that is cut at an angle.