Which of the following could be added to a solution of potassium fluoride to prepare a buffer? A) ammonia
B) potassium acetate
C) hydrochloric acid
D) sodium fluoride
E) sodium hydroxide

I think the answer will be sodium hydroxide and the reason why is because

Combustion is the act or process of burning. therefore, i believe the answer is  a: burning wood. 

The population of unionid mussels decreased after zebra mussels were introduced. zebra mussels competed with the unionid mussels for food. the zebra mussels were able to displace the unionid mussels, allowing the zebra mussel population to increase  over the years. the unionid mussel population decreased because  of lack of food.