According to the test, about what percent of teenage girls experience menstrual "cramping" with their menstruation?

Which of the following statements about cellular aging is true?

Cells can replicate indefinitely, but errors do occur. Aging may be caused by the inevitable loss of the ability of cells to duplicate perfectly. Damage is caused by free radicals that slow down the cell duplication process. Cells from adults are able to duplicate more quickly and more times than are cells from embryos.

"Look, Mom, she is not really happy; you can see it in her eyes!" cries Amelia's little sister. What might this sharp little 4-year-old have spotted?

A) A masked reaction B) A Duchenne smile C) A Pan Am smile D) A forced smile