Why it is not surprising that some species can interbreed with one another while others can not?

Grade 91.)the gravitational pull from the moon words).2.) what is the rate of gravitational 3.)if you drop a hammer, is it more likely to drop handle side down, head side down, or equal chance that it will land either way? why? 4.)a car moves 60km east and 90km west.a.) what is the distance the car traveled? b.) what is the car's displacement5.)what is the average velocity of a car that moved 60 km south in 3 hours? 6.) a car starts from rest and acceleration to 60 m/s over a time of 5 seconds. what is the acceleration of the car? 7.)what is the speed of an object at rest?