Hi!
Answer:
The answer is A.
Step-by-step explanation:
B and C- no you can't do that. It is not the proper way and you won't get the results you need.
The reason it is A is because you can either count for 1 min, or you can count the beats for 30 sec and then multiply those beats by 2 and you will get the correct data/count.
Hope this helps!