Which best describes why scientific models change over time?

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Below are the choices and the answer is B. 
a.) Models can be changed by scientists who are more famous than previous scientists. 
b.) As technology advances, new experiments often expose problems in accepted theories. 
c.) Scientists tend to value new theories because they are more exciting. 
d.) A newer theory is more valid because it uses more mathematics. 

Hypothesis. why don’t you know this? i learned this stuff in like 5th grade