In which one of the following combinations $(a - d)$ the number of chromosomes of the present-day hexaploid wheat is correctly represented?

• A
  Monosomic $\to 21$,Haploid $\to 28$,Nullisomic $\to 42$,Trisomic $\to 43$
• B
  Monosomic $\to 7$,Haploid $\to 28$,Nullisomic $\to 40$,Trisomic $\to 42$
• C
  Monosomic $\to 21$,Haploid $\to 7$,Nullisomic $\to 42$,Trisomic $\to 43$
• D
  Monosomic $\to 41$,Haploid $\to 21$,Nullisomic $\to 40$,Trisomic $\to 43$