TASK DEFINITION: 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.
PROBLEM: How many valence electrons does selenium have?  
 (A) 3 (B) 5 (C) 6 (D) 8

SOLUTION: C

PROBLEM: Tobias rode his bike on a road for a 2 hr period. On average, he passed a 1 km marker every 3 min during this period. Which of the following was his average speed for this 2 hr period?  
 (A) 10 km/hr (B) 15 km/hr (C) 20 km/hr (D) 25 km/hr

SOLUTION: C

PROBLEM: Della has a mixture of soil and water in a jar. Which of the following tools would best help Della separate the soil from the water?  
 (A) a filter (B) a measuring cup (C) a balance (D) a magnifying glass

SOLUTION:
A