Question

fiona wants to use the scientific method to answer the question \do oxygen levels in the air affect rates of photosynthesis?\ she reads about photosynthesis in her biology book and is ready to carry out the next step. what should she do next?
perform an experiment
design a procedure
make observations
form a hypothesis

Explanation:

The scientific method steps are: ask a question, do background research, form a hypothesis, design an experiment, perform the experiment, analyze data, draw conclusions. Fiona has asked the question and done background research (reading biology book). The next step is to form a hypothesis (a testable prediction about the relationship between oxygen levels and photosynthesis rate). Performing an experiment or designing a procedure come after forming a hypothesis, and making observations is part of earlier or later steps, not immediately after background research.

Answer:

form a hypothesis