Which are weak electrolytes?

The answer is not C. I tried this on angel, can't quite figure it out though. According to the textbook, (pages 130-131) NH3 is a weak base so definitely not A either as it doesn't include the weak base NH3. Cu(NO3)2 is ionic so that should be a strong electrolyte so all answers with 4 are out the window (D,E). So it looks like since we can eliminate A, C, D, and E. Leaving B as the correct answer.