Why are these statements true?

1. If n is a prime number and greater than two, then n is odd; so if n is greater than two and not odd, then it is not prime.
   
   
2. If there is overflow in this program, then an error message will print, but no error message printed; so there is no overflow.
   
   
3. Alfred will pass only on the condition that he will pass only if he concentrates implies he will pass.
   
   
4. A square is a rhombus, and a rhombus is a parallelogram; so a square is a parallelogram.
   
   
5. Socrates is a man, and all men are mortal; so Socrates is mortal.
   
   
6. Every natural number is a prime or not a prime.
   
   
7. There are infinitely many primes.
   
   
8. If 2/0 = 0 then 2 = 0.
   
   
9. Had Stalin developed the atomic bomb before anyone else, then we'd all be speaking Russian.
   
   
10. This statement is false.