Correct Answer: B

Rationale: Infants typically begin to smile in response to pleasurable stimuli by 2 months, which is an early sign of social interaction and emotional development.

Correct Answer: D

Rationale: The second dose of the hepatitis A vaccine is recommended 6 months after the first dose to ensure full immunity.

Correct Answer: A

Rationale: Rotavirus is the most common cause of diarrhea in young children, particularly those under the age of 2. Giardia, Shigella, and Salmonella can also cause diarrhea, but in the context of young children, Rotavirus is the primary pathogen responsible for diarrheal illnesses.

Correct Answer: B

Rationale: The correct answer is B. Acquired aplastic anemia in children is often caused by exposure to certain drugs, such as chloramphenicol or antiepileptics, which can lead to bone marrow failure and a decrease in all types of blood cells. Choices A, C, and D are incorrect because aplastic anemia is not commonly caused by deficient diet, congenital defects, or injury in children.

Correct Answer: C

Rationale: Dramatic play involves role-playing, allowing children to act out scenarios and become more comfortable with them. This type of play can help reduce anxiety about upcoming events like surgery. Cooperative play involves working together towards a common goal, associative play involves loosely interacting with others, and onlooker play involves observing others play without actively participating. These types of play are not as directly related to preparing a child for surgery and reducing stress as dramatic play.