I saw a couple of similar questions on chegg with answer picking the highest offer price as the National Best Offer Price. For this question, some expert picked A as the answer. I am very confused.

Time Exchange Bid Price Bid Size Offer Price Offer Size 9:30:00 NYSE 55.00 10,000 59.00 100 9:30:01 EDGX 54.75 200 55.33 100 9:30:02 BZX 50.00 300 62.00 1,600 9:30:03 NDAQ 54.88 100 61.00 100 9:39:00 NDAQ 52.00 100 63.00 100 9:40:45 EDGX 51.98 200 55.44 1,500 9:45:00 BZX 50.00 1,000 60.00 400 9:45:30 EDGX 51.98 400 54.32 600 9:46:55 BZX 50.00 200 60.01 900 9:50:05 EDGX 51.52 300 57.56 600 9:52:10 BZX 50.00 100 60.02 800 9:55:44 NYSE 51.99 300 55.34 600 9:59:59 BZX 52.00 100 56.00 100 At 9:56:00, what is the National Best Offer Price? a. NDAQ@63.00. EDGX@57.56. C. BZX@60.02. d. NYSE@55.34