instruction:
You are given a question, its answer, and a sentence that supports the question, i.e., the answer to the question is inferable from the sentence. In this task, you need to paraphrase the given sentence so that the paraphrased sentence still supports the question i.e. you can still infer the answer to the question from the paraphrased sentence. Do not write a paraphrase with a minor change in the given sentence e.g. replacing the word "one" with "a". Instead, try to write a paraphrase that contains new words, i.e. the words that are not present in the input sentence.
question:
Question: What type of mirror is shaped like the outside of a bowl? 
Answer: convex. 
Sentence: A convex mirror is shaped like the outside of a bowl.
answer:
A mirror is convex when it is shaped like the outside of a bowl.


question:
Question: Compounds containing which element are the basis of all known life? 
Answer: carbon. 
Sentence: Compounds containing the element carbon are the basis of all known life.
answer:
Carbon compounds are the basis of all known life.


question:
Question: The concentration of the hydrogen ion in a solution can be calculated when what is known? 
Answer: ph. 
Sentence: The concentration of the hydrogen ion in a solution can be calculated when the ph is known.
answer:

If the ph is known then the concentration of the hyrdorgen ion in a solution can be calculated.