Which two statements are valid objections to the experimental setup?
I. All the containers were filled with the same amount of water.
II. A different hot plate was used to heat water in different containers.
III. Water in different containers was heated for different amounts of time.
IV. The containers were not filled completely.

There is nothing wrong with I and IV. Using different hot plates can have an effect because some hot plates may be heating more efficiently than others. Heating water in all the containers for the same amount of time, rather than up to a fixed temperature, would be better because the rate of evaporation is the amount of water lost per unit of time. By using different times, the student is changing an important variable.