instruction:
In this task, you are given a question and answer for that. The answer will fill in the blank or will complete the unfinished question. Your task is to provide an explanation based on the given question or fill-in-the-blank statement, and answer.
question:
Question: A flu vaccine was administered to residents in a large city and the vaccine was effective in lowering the risk of flu among the residents. This means that the lower risk of disease resulted in a 
 Answer: lower death rate.
answer:
With better food and less chance of disease, the death rate fell.


question:
Question: Long ago the surface of Venus warmed enough that greenhouse gases escaped into the atmosphere. As a result, the greenhouse effect on that planet 
 Answer: increased
answer:
An increase in greenhouse gases leads to greater greenhouse effect.


question:
Question: If you need to turn a screw a few times that requires 
 Answer: less force
answer:

The trade-off when the threads are closer together, is that more turns of the screw or bolt are needed to do the job because the distance over which the input force must be applied is greater.