The Explanation:

External interrupts are used to interrupt the normal execution of a program and divert it to a specific routine or function. These interrupts are triggered by external events or signals, such as a button press or a sensor input.

The flags IE0 and IE1 are specific to the external interrupt sources in some microcontrollers or microprocessors. These flags control the enable/disable status of the external interrupt sources.

Level-Sensitive vs Edge-Sensitive:

In the context of external interrupts, there are two common types of interrupt triggering mechanisms: level-sensitive and edge-sensitive.

1. Level-Sensitive:
- Level-sensitive interrupts are triggered when a specific signal or level is present on the interrupt pin.
- The interrupt will be triggered as long as the signal remains at that level.
- It is suitable for interrupt sources that generate a continuous signal, such as a sensor output or communication line.
- Level-sensitive interrupts are controlled by flags that enable or disable the interrupt source.
- In this case, the flags IE0 and IE1 are used to control the enable/disable status of the interrupt sources, indicating that the interrupt programmed is level-sensitive.

2. Edge-Sensitive:
- Edge-sensitive interrupts are triggered by a change in the signal level on the interrupt pin.
- The interrupt is triggered when there is a transition from one level to another, either rising edge (from low to high) or falling edge (from high to low).
- Edge-sensitive interrupts are suitable for interrupt sources that generate a short pulse or a specific event, such as a button press or a signal edge.
- The control for edge-sensitive interrupts is typically handled by configuring specific registers or pins to detect the desired edge.

In Serial Port vs In Parallel Port:

- The options "c) in serial port" and "d) in parallel port" are unrelated to the type of interrupt triggering mechanism.
- Serial and parallel ports are different types of I/O interfaces used for data communication.
- Serial ports transmit data bit by bit sequentially, while parallel ports transmit multiple bits simultaneously.
- The choice between serial and parallel ports depends on the specific requirements of the system and the type of data being transferred.
- The interrupt triggering mechanism is independent of the choice of I/O interface.

Therefore, the correct answer is option "a) level-sensitive" as the flags IE0 and IE1 control the interrupt sources, indicating that the interrupt programmed is level-sensitive.