**Explanation:**

The dimensions of a physical quantity refer to the fundamental physical quantities that make up that quantity. If two quantities have different dimensions, it means that they cannot be expressed in terms of the same fundamental physical quantities.

Let's analyze each option to determine if the quantities have the same dimensions:

a) **Pressure, stress**: Both pressure and stress are defined as force per unit area. Therefore, they have the same dimensions, which are force divided by area. This option is incorrect.

b) **Velocity, speed**: Velocity and speed both represent the rate at which an object moves. They are defined as the change in position of an object over time. Therefore, they have the same dimensions, which are distance divided by time. This option is incorrect.

c) **Force, impulse**: Force is defined as the rate of change of momentum, while impulse is defined as the change in momentum. Momentum is the product of mass and velocity, so force and impulse have different dimensions. Force has dimensions of mass times acceleration (M * L * T^(-2)), while impulse has dimensions of mass times velocity (M * L * T^(-1)). This option is correct.

d) **Work, energy**: Work and energy are related to the transfer or transformation of energy. Work is defined as the product of force and displacement, while energy is the capacity to do work. Therefore, work and energy have the same dimensions, which are force times distance (M * L^2 * T^(-2)). This option is incorrect.

In summary, the only group of quantities in the given options that do not have the same dimensions is **force and impulse** (option C).