Which of these changes take place during labor? (i) rhythmic contractions of the uterus wall
(ii) opening of cervix
(iii) bag of liquid breaks
(iv) widening of the hips ​

The answer is rhythmic contraction of the uterus wall.

Explanation:

this is because when muscle is overly used, it brings about contraction

primary succession begins with a bare rock and ends with a forest secondary succession begins after a natural disaster where there is a temporary setback after a forest fire or local destruction, but the surrounding area can fill in

it also supports my hypothesis. if you rest first you can squeeze the clothespin more times. from the data i collected the average of the eight people concluded exercise makes your muscles more fatigued and less able to squeeze the clothespin compared to resting before squeezing.