A survey is considered valid if it measures what it is supposed to measure, because if it didn't measure what it was supposed to measure, it would lose it's credibility and not make any sense. The word that goes in the blank is "valid".
Im pretty sure the answer to your question is inertia
Answer: D. Both B and C
Explanation: While some people might want to be alone, others want someone to reach out to them and possibly help. D is the best option here.
The correct answer is known as "<span>Alzheimer’s-like spinal fluid proteins".
Alzheimer's Disease is known to be one of the usual classifications of Dementia. Alzheimer's Disease is a disease that worsens overtime, as a person with this illness continues to grow old, the disease worsens and disrupts their daily life, affecting their memories, cognitive abilities, such as communicating and thinking.</span>