Why do scientists only test one independent variable in an experiment?

What is the function of the nucleus in the euglena cells you observed?

Select all the correct answers. for a claim about the natural world to be considered scientific, what attributes must it have? a). it must be open to modification if new evidence doesn't completely support it. b). it must be based on scientific observations that can be repeated in a controlled setting. c). it must be applicable to future events and occurrences. d). it must be consistent with only a small portion of relevant observations or data.

What type of cell undergoes meiosis