Mendel published his work on the inheritance of characters in $1865$,but it remained unrecognized until $1900$ because:
$(a)$ He could not provide any physical proof for the existence of factors.
$(b)$ His concept of factors as stable,discrete units that controlled the expression of traits did not find acceptance from his contemporaries.
$(c)$ Mendel's approach of using mathematics to explain biological phenomena was considered ahead of its time and unconventional.
$(d)$ Communication was not easy (as it is now),and his work could not be widely publicized.

• A
  $(a), (b) \; \& \; (c)$ are correct
• B
  $(c) \; \& \; (d)$ are correct
• C
  $(a), (b) \; \& \; (d)$ are correct
• D
  Only $(a)$ is correct