You are given a science question (easy-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.

Which characteristic best identifies a pure substance?  
 (A) shape (B) texture (C) melting point (D) state of matter
C

Water at 20°C in an uncovered pan is evaporating very slowly. What could be done to the water to make it evaporate more quickly?  
 (A) Cover it. (B) Heat it. (C) Place it in the dark. (D) Put salt in it.
B

In 1921, Earl Dickson invented a bandage after he noticed his wife was unable to easily cover cuts on her hands. He covered the bandage with a chemical that sealed it so air would not enter the cut. How did solving this problem benefit others medically?  
 (A) People relied on bandages more than doctors. (B) The bandages cured cuts that were infected. (C) The bandages helped keep cuts clean. (D) People cut themselves less often.

C