Which of the following statements is NOT true: a) Light moving from a source moving toward the observer will have a higher frequency than if the source were at rest with respect to the observer.
b) The value of Hubble's parameter, H, is determined by measured redshifts of spectral lines for distant galaxies. c) Hubble's parameter, H, is used to estimate both the Universe's size and age.
d) According to Hubble's Law all galaxies must be moving away (receding) from our own.

D) according to Hubble’s law all galaxies must be moving away (receding) from our own.

This is all you, but i can give you some topics that you could try. if it rained when you want to do something outdoors, it 'limits' that human activity. maybe you want to do an experiment that goes throughout the whole year and you have to have above freezing the entire year. this 'limits' your activity. i thought of those just off of the top of my head. something that gets to me that might be getting to you is you are thinking too hard about what to do. think simply, and if it is too simple, then bump it up just a little bit.

Ca mega city if i’m not mistaken