**Drag and Lift Forces in Fluid Flow**

When an object is placed in a fluid stream, such as air or water, it experiences two main forces known as drag and lift. These forces are caused by certain factors within the fluid flow, namely pressure and viscosity.

**1. Pressure:**
Pressure is the force exerted by the fluid on the surface of the object. In fluid flow, pressure acts perpendicular to the surface. Two types of pressure are involved in the generation of drag and lift forces:

- **Static Pressure:** This is the pressure exerted by the fluid due to its weight and density. It acts in all directions uniformly, exerting a force on the object. The difference in static pressure between the front and rear surfaces of the object causes drag, which is the force that opposes the motion of the object.

- **Dynamic Pressure:** This is the pressure exerted by the fluid due to its velocity or motion. When the fluid flows around the object, it accelerates and exerts a force on the object in the direction of flow. This force is known as dynamic pressure. It is responsible for the generation of lift force, which is the force that acts perpendicular to the direction of motion and enables the object to rise or stay aloft.

**2. Viscosity:**
Viscosity is the internal resistance of a fluid to flow. It determines the fluid's ability to stick to the object's surface as it flows around it. Viscosity creates a shearing effect, causing adjacent layers of fluid to move at different velocities. This shearing effect gives rise to drag force, as the fluid resists the object's motion.

In summary, the drag and lift forces acting on an object in a fluid stream are caused by pressure and viscosity. Pressure, both static and dynamic, is responsible for the generation of drag and lift forces. Viscosity, on the other hand, contributes to the drag force by creating a resistance to the object's motion. Therefore, the correct answer is option 'A' – pressure and viscosity.