Answer:
a) Experiment designed to test hypothesis;
b) Hypothesis;
c) Observation.
Step-by-step explanation:
The scientific method is a list of procedures a scientist does to explain a phenomenon. The principal steps are:
1) Observation - In this step, the matter or the phenomenon is observed;
2) Problem elaboration - In this step, some questions about the phenomenon are made;
3) Hypothesis - The questions are answered, trying to explain the phenomenon;
4) Experimentation - The hypothesis is tested with experiments and the results are analyzed to determine if the hypothesis is or not correct.
Thus, first, it was observed that the combustion of a metal in a closed container ceases after a length of time (c); then the hypothesis made was that oxygen gas combines with a substance during its combustion (b); so the experiment is done: a metal is burned in a closed container and the change in mass of the solid and volume of the gas is measured (a).