Which of these is a mixture of elements?
a. silver and gold
b. carbon dioxide
c. salt and pepper
d. all of these are mixtures of elements.

A. silver and gold. Both silver and gold are elements. b is not correct because CO2 is a compound, not a mixture, and c is incorrect because salt and pepper are not elements.

Elements are pure substances that are found on the periodic table. 

Pepper is NOT an element. 
Carbon dioxide is a compound, not mixture. 
Next, gold and silver are both elements, so that may be the answer!

a) silver and gold

A) acceleration. this seems to be the one that makes sense.

The answer is water molecules are split.cellular respiration and photosynthesis are complement  reactions to each other. these are reverse reactions. in cellular respiration glucose and oxygen yield water and carbon dioxide. so, when respiration begins,  glucose molecules are split. in the opposite reaction - in photosynthesis, carbon dioxide and water yield glucose and oxygen. thus,  when respiration begins, water molecules are split.