A scientist wants to find the percent of teens that like the taste of "brand X" lemonade over "brand Y" lemonade. She conducts a taste test of 500 teenagers. She gives each teen a bottle of lemonade with the labels showing the brand of each lemonade. She asks each teenager to taste each brand after drinking water in between. She finds that 50% of teens like brand X and 50% like brand Y lemonade. Why are the results of the survey most likely unreliable? A. Adults were not interviewed.
B. Not enough teens were interviewed.
C. The investigation was based on taste.
D. The lemonade labels introduced bias.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.