Answer
a balance and a graduated cylinder
Explanation
Density is mass per unit and it is property  characteristic of a substance. The arrangement of the mass of atoms and their size is what determines the the density of a substance.
For a student to measure the density of seawater  he/she is required to use a balance and a graduated cylinder where a balance will be used to measure the mass of the mineral sample  and then a graduated cylinder to determine the volume.
 
        
                    
             
        
        
        
I’m sorry can u translate it to english!
        
             
        
        
        
Answer:
A) Silver maple
Explanation:
When looking at the food web, you can see that the arrow pointing at the beaver is going from the silver maple.
 
        
             
        
        
        
Answer:
50%
Explanation:
According to the given information, the allele for the red-green colorblindness is inherited in an X linked recessive manner. Let's assume that the allele X^c is responsible for red-green colorblindness. The woman is normal but had a colorblind father (X^cY). Fathers give their X chromosomes to the daughters while their Y chromosome is transmitted to their sons. The sons get their X chromosomes from the mother. 
The colorblind father has transmitted the X-linked allele for the red-green colorblindness to his daughter. Therefore, the genotype of the woman is X^cX. The woman would produce two types of eggs: 50 % with X^C and 50% with X. Therefore, 50% of sons of this woman would get X linked allele for the red-green colorblindness and would be affected by the disorder while the rest 50% of her sons will be normal. 
 
        
                    
             
        
        
        
I'm not saying this is for sure but this is what I'm answering for mine thanks to a yahoo answers.  d) Migrating bird populations and the carry capacities of local animal species. You don't have to award points or anything I just wanted to try and help. This is what I put on another persons questions as well. I hope this is helpful and accurate. I'm sorry if it is not.