According to the passage, what is NOT true about the first study().

A.More than 1,000 people took part in the study.

B.People who slept less had higher blood levels of ghrelin.

C.People who slept more had higher blood levels of leptin.

D.The amount of exercise can influence the result of the study.

珠光体力学性能主要取决于珠光体的片层间距，片层间距越小，则强度和硬度越高，塑性变形抗力越大。