Final answer:
Without further context or data, it's impossible to determine the initial number of students at lunch. For the electric-field lines question, a +20 nC charge should produce 20 electric-field lines since it's proportional to the +5 nC charge producing five lines.The correct option is D.
Step-by-step explanation:
To determine the initial number of students at the beginning of lunch, we need more context or data. The information provided in the student's query does not give a clear indication or a formula to calculate the number of students. Additional details such as the number of students who joined or left during lunch, or a numerical relationship describing the change in the number of students over time, would be required to provide an accurate answer.
In the case of the electric-field lines question, we can establish that the number of electric-field lines is proportional to the magnitude of the charge. Hence, if a +5 nC charge results in five electric-field lines, a +20 nC charge, which is four times greater, would be expected to produce 20 electric-field lines (d).