Which eras ended with a mass extinction?

Canada economy usa test prep i am stupid i don’t get it

Arecent poll of 500 residents in a large town found that only 36% were in favor of a proposed referendum to build a new high school. find the margin of error for this poll if we want 95% confidence in our estimate of the percentage of residents in favor of this proposed referendum.

Experiment to investigate effect of medication on levels of stress in males and females. dependant variable?