Sentence 1: Tanya wasn't too sure about this. 
 Sentence 3: All the other people in the room looked so fit 
 Sentence 4:  She tentatively began the aerobics class 
 Sentence 5:  Before she knew it she was having a blast 
 Option 1: She had signed up for the aerobics class but was now nervous. 
 Option 2: She had signed up for the yoga class but was now nervous.