Lele explored the relationship between the cleaning effect of chewing gum on oral cavity and chewing time. It is known that the main flora in the oral cavity are bacteria, actinomycetes and roots.

(1) According to the meaning of the question, this experiment is to explore the relationship between the cleaning effect of chewing gum on oral cavity and chewing time, so the variable of this experiment is the difference of chewing time;

(2) When counting, generally, five points are taken according to the plum blossom shape in each Petri dish, counted by colony counter, and the average of the five values is taken to ensure more accurate experimental data and reduce experimental errors as much as possible.

(3) In the experiment, the appropriate temperature is 37℃, because the temperature of the human body is 37℃, so as to ensure the same temperature as the oral cavity;

(4) According to the data in the table, when chewing 10 minutes, the number of colonies in the oral cavity is the least, so the best time for chewing gum is 10 minutes.

(5) In order to make the experimental results more accurate, it is suggested to shorten the chewing time and take samples every 2 minutes, so B is selected.

So the answer is:

(1) chewing time;

(2) Take the average value to reduce the experimental error.

(3)37℃;

④ 10 minute;

⑸B