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 typically involve asking a question, doing background research, then forming a hypothesis. Fiona has read about photosynthesis (background research), so the next step is to form a hypothesis to make a testable prediction about the question "Do oxygen levels in the air affect photosynthesis?". Performing an experiment or designing a procedure comes after forming a hypothesis, and making observations is part of earlier or later steps.

Answer:

form a hypothesis (the option "form a hypothesis")