Answer: Option A
Explanation:
Rheumatic fever is a disease which affects the joints of the body. It also affects the skin and brain of the body.
Rheumatic fever symptoms is very similar like the common cold and fever. This fever can also occur after the throat infection which is caused due to group of bacteria known as Streptococcus.
It has the ability to cause sore throat, scarlet fever and infections in different parts of the body.
Rheumatic fever takes places if the strep throat and scarlet fever is not treated on time.
The answer is B, matrix of the mitochondria
1. Testing only one variable
A controlled variable means its the one that stays the same. In a controlled experiment, it means there is only one manipulated, (changed) variable.
I would say oxygen because respiration is breathing mechanically.
