Answer:
1 = A
2 = B
3 =  B
Explanation:
1) Black holes occur when really big stars collapse on themselves. And, in order to get big, the star has to be an old one.
2) A black hole is something huge that swallows up everything, while a protostar is just the very beginning of a star.
3) Scientist can't truly know for sure, but they can infer about them due to the effects of the surrounding areas.
 
        
             
        
        
        
The benefits are Beaches are better protected against erosion.
Trenches created in the ocean encourage species growth. 
WhatWhat are the advantages and disadvantages of beach nutrition?
Since nutrition just reduces the consequences of erosion and does not address its origins, it is usually a recurrent procedure. An agreeable setting lengthens the time between nutrient projects, cutting costs. On the other hand, a high rate of erosion might make nutrition unprofitable.
Sea turtles and rare and endangered birds alike depend on healthy beach and dunes systems. Important wildlife habitat areas that are endangered by erosion are provided by maintaining nourished beaches. 
To learn more about Beaches refer 
brainly.com/question/15524787?
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Answer:
Nitrate deficiency
Explanation:
Plants absorb nitrates in water through their roots. Nitrates are present in high levels in plant fertilisers. Without nitrates, the amount of chlorophyll in leaves reduces. This reduces the plant's ability to photosynthesise and grow properly, which reduces the farmers' crop yield .
 
        
             
        
        
        
Viruses are made of one or more nuclei acid molecules surrounded by a coat protein or capsid. So the core of the virus will contain the viral genome. Some viruses' capsid maybe enclosed with an envelope derived from the host cell (the cell that the virus is infecting), and this envelope is also derived from the host cell membrane.
        
                    
             
        
        
        
The two stages of photosynthesis: Photosynthesis takes place in two stages: light-dependent reactions and the Calvin cycle (light-independent reactions). Light-dependent reactions, which take place in the thylakoid membrane, use light energy to make ATP and NADPH.