Final answer:
Question A, 'What is the family's annual income?' is least important for a teacher to understand a low-income child's background, as it offers less direct insight into crucial factors affecting their school performance.
Step-by-step explanation:
To understand the family background of a low-income child who is having difficulty in school, certain questions are more pertinent than others. When considering socioeconomic status, mutual respect, family support, and unusual responsibilities, question A, 'What is the family's annual income?' is the least important for a teacher. Knowing the exact annual income does not provide direct insight into the child's home environment, emotional support, and whether the child needs to take on additional responsibilities - all factors that are more crucial to understanding the child's circumstances and how they may impact educational attainment.