Answer:
C. spectrum used by most mobile phone firms that does not travel well through solid objects.
Step-by-step explanation:
Obstructions on the path of radio waves can result to poor network coverage. This is also called Phone reception or coverage black spot. Just as an obstruction on the path of light waves causes the emergence of shadows, so also an obstruction from waves coming from the cell tower. Common culprits are windows, doors, roofing materials, and walls. These solid objects cause an interruption of network for network providers inside a building.
The use of antennas connected from outside the building to inside can be helpful in reducing the effect of this obstruction. Problems resulting could be low signal, difficulty hearing a caller at the other end, slow internet connection, etc.