Read the following passage and mark the letter A,B,C or D on your answer sheet to indicate the correct word for each of the blanks from 1 to 5.

Swim, Cycle, and Run

    For athletes who like to (31)______a variety of endurance sports in a single race, triathlons are a great fit. These competitions (32) ______running, cycling, and swimming into one race, and they take place one after the other in a single continuous timed race. Athletes who participate must be in top physical form and have the skills needed to complete each portion of the race.
    Training for triathlons means the athletes have to become proficient not only in the sport required in each stage, but they also have to become familiar with what (33) ______from one to the other does to their bodies. Many inexperienced triathletes are surprised to (34) ______hard it can be to switch from swimming to cycling to running, and how tired their muscles can suddenly feel. One thing all triathletes can agree (35) ______is that no one ever told them that running a triathlon would be easy

Điền ô số 34

A. find what

B. find out why

C. find out how 

D. find how