A.I. Explanation:

Option 1: "Over 250 million children are not acquiring basic skills in school"

Explanation: The text states that over 250 million children in school are not learning basic skills, which directly addresses a major issue affecting children's education. This aligns with the overall theme of the text, which emphasizes the challenges in education.

Option 2: "Lack of professional training for teachers"

Explanation: This option is not mentioned in the text. The text focuses on the number of children affected by educational issues rather than the qualifications of teachers. Therefore, it does not provide relevant information.

Option 3: "61 million children are not in primary school"

Explanation: The text explicitly states that 61 million children are not in primary school, highlighting a significant barrier to education. This fact supports the main idea of the text regarding the lack of access to education for many children.

Option 4: "High cost of school materials"

Explanation: This option is not supported by the text. There is no mention of the cost of school materials as an issue affecting children's access to education, making this statement irrelevant to the context.

Option 5: "15 million children are working instead of attending school"

Explanation: The text indicates that 15 million children are working rather than attending school, which is a critical issue affecting their access to education. This aligns with the text's focus on the various challenges children face in obtaining an education.