How is the gender of a person determined genetically? Please give a good answer with proof because I'm failing school and don't want to get held back and if I get a B+ I pass school. I also put all my points.

Ascience research group is testing a new type of plant food. one trial is conducted in a controlled experiment. the data from the trial show that the plant that received the new food grew faster than the control plant. the group announces that the new plant food makes plants grow faster. what is the main weakness in this scientific claim?