You will be given a definition of a task first, then some input of the task.
Given a prompt and four completions, select the completion that is the most plausible in continuing or answering the prompt. This task is designed to test common sense and has various categories ranging between idioms, negated statements, polysemy, subject referencing, and quantitative reasoning. Generate either Completion A, Completion B, Completion C, or Completion D.

Prompt: This is a complex problem because 
Completion A: it can be solved easily. 
Completion B: we solved it quickly. 
Completion C: everyone can solve it. 
Completion D: we are not able to solve it.
Output:
Completion D