"what will cause the time period of the fixed amount settlement option to be extended? "

An increament in the interest credited.

Explanation:

Only an increament in the interest would cause the time period of the fixed amount settlement option to be extended.

answer; black& white dialogue;

it might look like that the ideal way to research the health effects of trans fats is through a controlled experimental feeding trial. but these kinds of trial have several important limitations that the researcher must look into:

short in duration (this factor usually checks up on the intermediary risk factors rather than the actual outcomes of the disease)

limited dietary changes

only makes use of healthy participants