How many protons does an atom of oxygen have

Astudent observes a star from two positions of earth in its orbit, in summer and winter, and measures the change in the position of the star. which of these can be best calculated by this method?

When does the circulatory system work with the respiratory system? a. during blood cell formation b. during cellular respiration c. during intestinal digestion d. during a viral infection

Abrown coat is recessive in labradors, while a black coat is dominant. if two hybrids are bred, what percentage of the offspring will have black coats? a. 25% b. 50% c. 75% d. 100%