Introduction:
The Laplace Transform is a mathematical tool used to analyze linear time-invariant systems. It is commonly used in various fields such as electrical engineering, control systems, and signal processing. The Laplace Transform converts a time-domain signal into a complex frequency-domain representation, allowing for easier analysis and manipulation of the signal.

Unilateral Laplace Transform:
The unilateral Laplace Transform is defined for signals that are causal, meaning they are zero for negative time values. It is commonly denoted by the symbol "U(s)" and is given by the integral:

U(s) = ∫[0, ∞] u(t)e^(-st) dt

where u(t) is the time-domain signal and s is the complex frequency variable.

Bilateral Laplace Transform:
The bilateral Laplace Transform is defined for signals that are non-causal, meaning they are non-zero for both positive and negative time values. It is commonly denoted by the symbol "X(s)" and is given by the integral:

X(s) = ∫[-∞, ∞] x(t)e^(-st) dt

where x(t) is the time-domain signal and s is the complex frequency variable.

Difference between Unilateral and Bilateral Laplace Transform:
The main difference between the unilateral and bilateral Laplace Transform lies in the range of integration. The unilateral Laplace Transform only considers the positive time values (t ≥ 0) while integrating the signal, whereas the bilateral Laplace Transform considers both positive and negative time values (t ∈ [-∞, ∞]).

Useful Signals:
a) d(t) - Dirac delta function or impulse function
b) s(t) - Step function or Heaviside function
c) u(t) - Unit step function
d) All of the mentioned

Explanation:
The Dirac delta function (d(t)), step function (s(t)), and unit step function (u(t)) are all non-causal signals. They are non-zero for both positive and negative time values. Therefore, their Laplace Transforms would be evaluated using the bilateral Laplace Transform.

The Dirac delta function has a Laplace Transform of 1, regardless of whether it is evaluated using the unilateral or bilateral Laplace Transform.

The Laplace Transform of the step function is given by:

S(s) = 1/s

Similarly, the Laplace Transform of the unit step function is given by:

U(s) = 1/s

In both cases, the Laplace Transform can be evaluated using either the unilateral or bilateral Laplace Transform, and the result would be the same.

Therefore, in the case of the given signals, namely d(t), s(t), and u(t), the bilateral Laplace Transform is different from the unilateral Laplace Transform. Hence, the correct answer is option 'C' - all of the mentioned.