in a scientific experiment, how many independent variables should be tested
at the same time?
o a) none
ob) one
oc) two
od) three or more

The correct option is b) one

Explanation:

An independent variable can be described as a variable which is changed or varied in order to test its effect on the dependent variable. Although multiple variants can be changed at a certain time but it is best to change and see the results of one independent variable at a time. This will allow more valid results to be deduced. Hence, accurate results can be made if one variable is changed at a time.

that is wrong, its not thymus.