Answer: A.
Explanation:Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a ... Between each pulse, the radar station serves as a receiver as it listens for ... If pulses are emitted too frequently, the returns from one pulse will be ... Over the area covered by radar echoes, a program assigns a precipitation type
Answer:
1-C............. ...............
No they cant be mechanical because then something would have to generate their rays through the inventing of a machine.
They provide the immune system with "memory" against previously encountered pathogens.
T memory cells are necessary for protective immunity against invading pathogens
Oxygen entered the Earth's atmosphere after the appearance of the Great Oxidation Event (Great Oxygenation Event). The Great Oxidation is the first mass extinction on Earth.
The Great Oxidation lasted 2.4 to 2.0 billion years ago.
Oxygen appeared on Earth thanks to cyanobacteria using photosynthesis.