Agrobacterium infects plants and causes them to form tumors. You are asked to determine how long a plant must be exposed to these bacteria to become infected. Which of the following experiments will provide the best data to address that question?
A) Measure the number of tumors formed on a plant when exposed to various concentrations of Agrobacterium.
B) Measure the number of tumors formed on plants, which are exposed to Agrobacterium for different lengths of time.
C) Determine the survival rate of Agrobacterium when exposed to different concentrations of an antibiotic.
D) Measure the concentration of Agrobacterium in different soil environments where the plants grow.

In an experimental procedure, the independent variable brings a change over the dependent variable. The changes in the independent variable can be done manually, which exerts it's influence over the dependent variable.

Here the time duration to which the plant is required to be exposed so that it receives a bacterial infection is required to be determined. Thus b is the correct option. This is because of the fact that infection will result in tumors which is dependent variable caused by the different length of time of exposure of the plant to the Agrobacterium which is the independent variable.