The dominant trait is hornless. 
If this is correct, then the original bull is a heterozygote:
H = hornless
h = horned
Bull is Hh
Cross 1: Hh x hh (horned female) - offspring is hh (horned)
Cross 2: Hh x Hh (hornless female) - offspring is hh (horned)
Cross 3: Hh x hh (horned female) - offspring is Hh (hornless)
Cross 3 is the key to confirming this because the only way to get a hornless offspring would be if hornless is recessive.
        
             
        
        
        
Answer:
Ectoparasites are organisms that live on the skin of a host, from which they derive their sustenance. The phylum Arthropoda includes the two-winged, or dipterous, flies. The larvae or maggots of these flies may invade the living or necrotic tissue of animals and humans, producing myiasis. Multiple dipterous flies are thought to be capable of producing ocular myiasis. It is thought that the larvae are embedded in the eye, that they burrow directly through the sclera and then under the retina. Typically, they leave asymptomatic tracks throughout the fundus, but a number of cases of destructive endophthalmitis have been reported, particularly from Scandinavia.
 
        
             
        
        
        
He tricks persuades him by giving home candy
        
             
        
        
        
The factor being tested is the variable. There are two types of variables, independent and dependent. The independent variable is the factor being changed by the scientist or the person controlling the experiment. The dependent variable is the thing that gets changed due to the changing of the independent variable. The dependent variable cannot be changed physically by the person doing the experiment.
 
        
             
        
        
        
I'd say your answer is, 
C. the attraction and bonding of ions with equal opposite charges.