After researching the possible effects of music, Elaina proposes that if people listen to faster-paced music, their pulse rates will increase more than if they listen to slower music. Her mother listens to classic rock at a high volume for 30 minutes, her younger brother listens to classical music quietly while he sleeps at night, and her grandmother listens to two hours of rap at a medium volume. Elaina records each person's pulse before and after listening to the music. What is missing from Elaina's scientific investigation?

Constant variables

Explanation:

Elaina's investigation lacked the critical ingredient of constant variables which are important components of every scientific investigation. In every research, there are 3 important variables, namely:

1. Dependent variables: the actual variable to be measured during the course of investigations and whose values are dependent on another variable (independent variable) supplied by the investigators.

2. Independent variable: one of the variables that are supplied by investigators whose values are often manipulated to see the kind of changes it will cause to the dependent variable.

3. Constant variables: other variables that are neither independent nor dependent but constant for all the various experimental groups in investigations.

the father in the first generation probably had the recessive colorblind trait in his x chromosome. if he and his wife both had the colorblind trait, even if she had 1 recessive and 1 dominant, then that trait would be passed on to their kids.

(since you didn't attach the family tree this is just an assumption)

coal is not sustainable because it will one day run out.