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I’m aware of this and it’s irritating and unsettling.

It’s difficult – the easiest way is to refrain from affecting them psychologically of course.

The longer you spend in their presence, the harder it is to avoid their attention.

Importantly though, you need to learn to turn your own "eye" outwards, it’s a powerful tool at your disposal and you should not waste it looking for faults within yourself.

Seriously, it’s irritating to be aware of this..

Convince them that you are not there. If they think you are not there, they will not see.

On the internet, I can hear ads and shows that I can not find on the screen. They are unseen. How do you get rid of them? Sometimes they do not disappear when I log off the internet. What do I do and what can this be?

You have a virus. Download an Antivirus, such as AVG, Avast, or Alwil, and get rid of the viruses.

that the companion is much fainter than the G star, so it cannot be seen next to the brighter G star). By measuring the velocity of the G main-sequence star and the period of its orbit, you estimate that the combined mass of the two stars is 3 solar masses. The unseen companion is probably a
A) red giant
B) white dwarf
C) neutron star
D) O main sequence star
E) black hole

"G" means that the star that can be seen is pretty "average" Sun-like star.

Hence, by process of elimination, the companion star can not be:
- a red giant because red giants are more luminous and hence it would be easily visible
- O class main sequence star because these are some of the brightest and most massive stars, so it would be visible, too, and the total mass of the system would be well over 3 solar masses.
- white dwarfs are small star with little mass, limited to 1.4 solar masses. Given that the "invisible" companion is approx. 2 x the mass of the visible star, it can’t be a white dwarf.

So now we are down to two choices – neutron star and black hole. Neutron stars are strong sources of X-rays but relatively dim in visible spectrum. Because the question does not specify if the detection in limited to visible light only or the entire electromagnetic spectrum, neutron star COULD be the "invisible" companion. This could be easily confirmed by taking a "snapshot" of the system in the X-ray part of the spectrum.

Finally, if the system is not a strong source of X-ray radiation, than the only choice left is a black hole. However, black holes in the range of two solar masses are not very common. Theoretically they can exist, but the smallest black hole positively identified to date is about 3.8 solar masses.

Net, this is a typical high school or introductory astronomy question from a course given by somebody who probably has a very limited knowledge of astrophysics and is teaching "by the book".