Fill in test

[Samhu]

Hi Erin,
It is the first time I visit this forum. I've been studying English for a couple of years and I lik solving tests. Yesterday I found a rather curious one. Although I know the solution of this test, I cannot find the explanation why it is that. Here is the problematic one: Choose the wrong one!
"By the time you grow up, there --------- professions where you can manage without a personal computer.
a. may not be any b. won't be any c. could be no d. can be no
The solution as per the book is "d".
Please explain it to me, why?
Thanks in advance, Samhu