The effects on tomato production of leaves mixed in with the soil are being investigated. In the research an identical quantity and type of soil was placed in four large pots. However, 15 kg of mulched leaves were added to the first pot, 10 kg to the second and 5 kg to the third. No mulched leaves were added to the fourth pot. Tomatoes were then planted in these pots. All the pots were placed in sunlight and watered identically. Tomatoes obtained from each pot were weighed and recorded. What is the hypothesis that was tested in this research?
a. Plants produce tomatoes in proportion to the sunlight they receive.
b. The larger the pots are the more mixed leaves are needed.
c. The more water in the pots, the faster the leaves rot.
d. The more mulched leaves are in the soil the more tomatoes are produced.

Research hypotheses are:
a. Formulated prior to a review of the literature
b. Statements of predicted relationships between variables
c. B but not A
d. Both A and B