Option C too.
C) Grab it when expired
Back to Option B. Yes, they can accuse you. It is a free country. However are they legally correct in their statement about you. That answer depends on a few things. Who they are and what they have done to protect themselves and also what you do with the name. If they are Microsoft and you want Microsoft.net then I think you see the answer is clear. Microsoft is the owner of the Microsoft trademark. Any use offline or online use will have their lawyers on you.
Now, if this is company X that just register domain y then they may not have protected themselves. So you are clear. But the real catcher is they may not be big enough even if they get registered trademarks.
For example, If I am big-store.com in Utah with registered trademarks nation wide for big-store. Then your natural reaction is that they are the same as Microsoft. However, some recent rulings have said if your company is not big enough globally then you really don't have rights to that trademark or domain name outside your own area. So if you have never heard of the company then you are pretty safe.
However, the third part of this is what you do with the name. If you registered big-store.net and big-store.com sells just underwear online. Then you start selling just underwear online then you are clearly on legally shaky ground.
But the short answer to your question, You should be fine.
PS: there are some great threads on Option C.