You are testing 3 new herbicides, A, B, and C, to control itch grass and to compare the effectiveness of the herbicides with a currently used herbicide, Round-Up, and the treatment with just water. Which of the following is considered as a positive control?

Round-Up

Explanation:

In one experiment the positive controls are used in order to validate the evaluation of the test, which is done in this case to measure the effectiveness of the herbicides. The researchers previously found that the herbicide Round-up controls the herb and has a high effectiveness , making this positive positive control be compared with the experimental results. In a positive control we have the desired effect in this case the elimination of grass.

not sure if this what   you'r looking for would be percent composition