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.

[EX Q]: Similar types of cells form tissues. What is the next level of complexity formed from the grouping of tissues?  
 (A) organs (B) organelles (C) organisms (D) organ systems
[EX A]: A

[EX Q]: When air rises over the open ocean, a low pressure system is formed. Which factor increases the potential of a low pressure system developing into a hurricane in the Northern Hemisphere?  
 (A) cool ocean currents circulating towards the equator (B) increased volcanic activity in the upper latitudes (C) cold air moving south from the North Pole (D) warm water temperatures in the tropics
[EX A]: D

[EX Q]: Which reaction is endothermic?  
 (A) cold pack (B) coal burning (C) striking a match (D) charcoal grill fire
[EX A]:
A