The best way is that u need not study the themes . dont waste ur time. u woud get 1 minutes extra for cooing after the question papers are given right?. so use that time to read the question and find the answer for the otba section.if u follow the pattern of b,c,d,a , you will get a lot of time and trust me , i did this the same way and it worked out.
but if u r nervous that u this wont help u then just summarise the themes and just chill.all is well