And a more difficult one, if the projects in my companys are only using MFC, would it be desirable to hire someone who only know C#/VB.NET?
The syntax is not important, the way you solve problems is. And the only one who can teach you how to solve problems is yourself. Your teacher can help you discover these problem solving abilities, but you will have to find your own unique way. Otherwise you are just a copycat and never be as good as your teacher.
If you don't know the syntax, sometimes you can't read/debug code.
Just imagine the shock when I see an one-liner that's a mix of LINQ plus anonymous functions. Books won't show you every example, and you can read it if the you can't understand the syntax, especially if some of the types involved in that query is coded as dynamic type. Possibly even Intellisense can't help you in the case.
Now try add extension methods to the mix.
Btw, the aim of traditional exams are to assess 1) how much you can remember from the lessons; 2) how well you can apply what you learnt. Calculators (or I should say, computers) that carries these information kind of defects the first aim.