Running time of a program depends on:

a) Addressing mode:
The addressing mode refers to the way in which the operands of an instruction are specified. Different addressing modes have different efficiency levels in terms of accessing data from memory. For example, direct addressing mode allows direct access to memory addresses, which can be faster than indirect addressing mode where additional memory accesses are required. Thus, the choice of addressing mode can impact the running time of a program.

b) Order of computations:
The order in which computations are performed can greatly affect the running time of a program. For example, if a program performs a series of expensive computations before checking a simple condition, it may waste unnecessary computation time. By rearranging the order of computations, it is possible to optimize the program and reduce the running time.

c) Usage of machine idioms:
Machine idioms are specific instructions or programming constructs that are known to be more efficient in terms of execution time. These idioms take advantage of the underlying architecture of the computer system to optimize the program. By utilizing machine idioms, the running time of a program can be significantly improved.

d) All of the mentioned:
All of the mentioned factors (addressing mode, order of computations, and usage of machine idioms) can collectively impact the running time of a program. Each factor plays a role in determining the efficiency and performance of the program. Therefore, considering all these factors is crucial in optimizing the program's running time.

In conclusion, the running time of a program depends on a combination of factors such as addressing mode, order of computations, and usage of machine idioms. By carefully considering and optimizing these factors, the overall performance of the program can be improved.