To determine the order of the genes on the chromosome, an interrupted mating study is carried out between the Hfr donor strain, leu+ pro+ trp+ his+, and the recipient, leu- pro- trp- his-. After conjugation is established, a small sample of the mixture is collected every minute for 20 minutes and the results obtained are as follows: Leu - 8 minutes, trp - 17 minutes, his - 12 minutes, and pro - 0 minutes. Which of the following is the correct order of sequence?