Explanation:
Control transfer instructions are used in computer programming to alter the flow of control or the sequence of instructions being executed. These instructions allow the program to jump to a different location in the code, enabling the execution of different sections of the program based on certain conditions or criteria.

Control transfer instructions can be categorized into two main types: explicit and implicit control transfer instructions.

Explicit Control Transfer Instructions:
Explicit control transfer instructions are those instructions that explicitly specify the target location or address to which the program should jump. These instructions are used when the programmer wants to transfer control to a specific location in the program, irrespective of any conditions.

Examples of explicit control transfer instructions include:

1. GOTO: This instruction transfers control to a specified label or line number in the program. It is considered a direct and unconditional transfer of control.

2. CALL: This instruction is used to call a subroutine or a function in the program. After executing the subroutine, control is transferred back to the instruction following the call.

Implicit Control Transfer Instructions:
Implicit control transfer instructions, on the other hand, transfer control based on certain conditions or criteria. These instructions alter the flow of control based on the outcome of a logical or conditional test.

Examples of implicit control transfer instructions include:

1. Conditional Branching Instructions: These instructions transfer control to a different location in the program based on the result of a logical or comparison operation. Examples include IF-THEN-ELSE statements and switch-case statements.

2. Unconditional Branching Instructions: These instructions transfer control to a different location in the program without any condition. They are typically used for loops and other repetitive structures. Examples include the WHILE loop and the FOR loop.

Therefore, the correct answer is option 'B' - conditional and unconditional control transfer instructions. These two categories cover the different types of control transfer instructions that are commonly used in computer programming.