The answer is option 'B', L-band.

The Global Positioning System (GPS) is a satellite-based navigation system that provides location and time information to users all around the world. It relies on a network of satellites orbiting the Earth to transmit signals that can be received by GPS receivers.

GPS carriers use the L-band frequency band for transmitting their signals. Here is an explanation of why L-band is chosen for GPS carriers:

Frequency Band Characteristics:
- Different frequency bands have different characteristics in terms of signal propagation, interference, and antenna size requirements.
- The L-band frequency range falls between 1 to 2 GHz, which is in the microwave region of the electromagnetic spectrum.
- Microwave frequencies are commonly used for satellite communication due to their ability to penetrate the Earth's atmosphere and experience less interference from weather conditions.

Advantages of L-band for GPS:
1. Signal Penetration: L-band signals have a good ability to penetrate through various obstacles such as buildings and tree canopies. This makes them suitable for providing accurate positioning information even in urban areas or dense forests.

2. Interference: L-band signals experience less interference from atmospheric conditions, such as rain or fog, compared to higher frequency bands. This ensures reliable signal reception and reduces the chances of signal degradation.

3. Antenna Size: The wavelength of L-band signals is relatively large compared to higher frequency bands. This allows for the design of smaller and more compact GPS antennas, making them easier to integrate into handheld devices or vehicles.

4. Availability of Frequencies: The L-band frequency range is allocated specifically for satellite navigation and positioning systems like GPS. This ensures that the frequencies are reserved and not heavily congested with other communication systems.

5. Global Coverage: The GPS system is designed to provide global coverage, and L-band signals are capable of traveling long distances without significant degradation. This allows GPS receivers to obtain accurate positioning information anywhere on Earth.

In conclusion, the L-band frequency band is used by GPS carriers due to its advantages in signal penetration, interference resistance, compact antenna design, availability of frequencies, and global coverage capabilities.