False. Their exoskeletons are made of silica.
        
             
        
        
        
Answer
          The arm and base of microscope are connected with each other with help of inclination joint. which provide easiness to user during research analysis or other microscopic studies. 
It has significant role in light and compound microscope that need light for visualization of examine sample. It also help in easy rotation during focusing toward light for better contrast. 
 
        
             
        
        
        
Answer:
The energy flow in the ecosystem decreases as it flows from one trophic level to the next trophic level. Only 10% of the energy will transfer to the next trophic level and the remaining energy is lost in the other metabolic process.
The energy flow in the case of the grassland can be shown by the trophic relationship of the organisms. The sun is the primary source of the energy that are absorbed by the plants through the photosynthesis process. The cattle acts as herbivores will consume the plants energy by directly feeding on them. The ranch should be protected from the other animals that feeds on cattle and they are known as carnivorves. 
 
        
             
        
        
        
Answer:
A) Light pollution both attracts and repels migratory birds
In addition to the many hazards that exist in urban areas, cities typically lack the food resources and cover that birds need during migration or when raising their young. ... Darkening skies at night during migration season makes it easier for birds to navigate.
Explanation:
Migration carries high costs in predation and mortality, including from hunting by humans, and is driven primarily by availability of food. It occurs mainly in the northern hemisphere, where birds are funneled on to specific routes by natural barriers such as the Mediterranean Sea or the Caribbean Sea.
 
        
             
        
        
        
The number of weight gained in pregnancy should be different based on the BMI. Assuming Sadie BMI is 25-29.9kg/m2 then the normal weight gain for single pregnancy would be 15 to 25lbs. 
Higher BMI will cause the normal weight gain become lower. For BMI >30kg/m2 normal weight gain would be 11-20lbs