A
It’s the most straightforward so that is probably the answer. I can’t see how you could get a more accurate answer other than literally timing each board
Sorry, I'm not sure.
I would suggest asking a trusted adult or teacher or redoing the lesson. Cheating isn't a good path: you will not do well in the future if you always search for answers on the internet.
Answer:
2.B-mining and drilling has increased 3.D -migration