Astudent reads the label on the bottle of salad dressing shown below.
ingredients
oil, vinegar, spices
directions: shake well
before using. refrigerate
after opening.
why would the student shake the salad dressing well before using it?
a. vinegar and oil have different densities
b. vinegar and oil easily form a solution
c. vinegar and oil both contain water
d. vinegar and oil are both liquids

The best option is a. but it is not complete!

Both liquids have different densities, it's true. But they are immiscible liquids and they don't form a solution.

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant.