Answer:
d. The two species have a different number of chromosomes, resulting in a postzygotic barrier.
Explanation:
The two species i.e. sheep and goat have different number of chromosomes that resulting in a postzygotic barrier. Sheep has 56 number of chromosomes whereas goat has 60 number of chromosomes that causes postzygotic barrier in the offspring produced from the fusion of these two species. Postzygotic barrier leads to the creation of a hybrid that is sterile and unable to produce offspring because of difference in chromosome number.
 
        
             
        
        
        
Answer: D
Explanation: over the courses of time, we discover more and more explanations for causes of chemical reactions, biology, etc.
 
        
             
        
        
        
Answer:
Artificial reproduction such as embryo transfer is one reproductive technology that has been beneficial to the livestock producers. There are various methods by which artificial reproduction can be achieved:
- Artificial insemination: It is the process by which semen can be introduced into the females so that fertilization can occur.
- Embryo transfer: By this techniques embryos can be implanted into the female and reproduction be made possible.
These technologies benefit the producers by crossing those species which have better traits and can pass these traits to the offspring through these techniques. 
 
        
             
        
        
        
The sperms exit testes through ureter which is a common urinogenital duct: ureter delivers sperms in cloaca. In female frogs, ovaries shed the mature eggs in coelomic cavity. Eggs enter oviducal funnel to reach oviduct.