Unlike human runners, who broke the four-minute mile in 1954 and they consistently recorded faster times ever since, horses in classic races such as the Kentucky Derby have had winning times with little improvement: Secretariat's world-record-breaking Derby tine of 1:59 2/5, for example, was set in 1973 and remained unsurpassed more than a quarter of a century later.

• Athey consistently recorded faster times ever since, horses in classic races such as the Kentucky Derby have had winning times with little improvement  
• Bthey have consistently recorded faster times ever since, those of horses in classic races such as the Kentucky Derby have shown little improvement in winning times  
• Chave consistently recorded faster times ever since, horses in classic races such as the Kentucky Derby have shown little improvement in winning times  
• Dhave consistently recorded faster times ever since, in those of classic races such as the Kentucky Derby, horses have had winning times with little improvement  
• Econsistently recorded faster times ever since, those of horses in classic races such as the Kentucky Derby have shown little improvement in winning times