You will be given a definition of a task first, then some input of the task.
You are given a science question (hard-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

Examine each of these chemical equations to determine which equation is correctly balanced.  
 (A) Mg(NO_{3})_{2} + K_{2}CO_{3} -> MgCO_{3} + KNO_{3} (B) Mg(NO_{3})_{2} + K_{2}CO_{3} -> MgCO_{3} + 2KNO_{3} (C) 2Mg(NO_{3})_{2} + K_{2}CO_{3} -> 2MgCO_{3} + KNO_{3} (D) Mg(NO_{3})_{2} + 2K_{2}CO_{3} -> MgCO_{3} + 2KNO_{3}
Output:
B