The correct answer is A. Trowel.
A trowel is a hand tool used to apply mortar to bricks and other masonry units. It is a flat, rectangular blade with a handle. The blade is typically made of steel or iron, and the handle is made of wood or plastic.
A trowel is used to lift mortar from a bucket or mortar board and spread it on the surface of a brick. The trowel is also used to form the joints between bricks.
A trowel is an essential tool for bricklaying. It is used to apply mortar, form joints, and smooth the surface of bricks.
The other options are not as important as a trowel for bricklaying.
A square is used to check the alignment of bricks. It is a flat, rectangular tool with two perpendicular sides.
A bolster is a heavy hammer used to break bricks. It is a long, thick bar with a flat head.
A scutch is a tool used to smooth the surface of bricks. It is a small, flat tool with a handle.