7.Professor Chauvet has 6 snake plants at her home. Two are small, two are medium, and two are large. She wants to see if the plants will grow taller if they are given water from her fish tank. She puts all the plants in her bay window at home so they receive equal amounts of sunlight. For the two small plants, she flips a coin to determine which one will get the water from the fish tank. She does the same for the medium, and large plants. She waters them this way weekly for 10 weeks. After 10 weeks she compares the difference in growth for each set of 2 plants. Which of the following is the best description of the method she is using for data collection?
(A)An observational study
(B)A double-blind observational study
(C)An experiment with a completely randomized design
(D)An experiment with a randomized block design
(E)An experiment with a matched-pairs design