Answer: The correct answer is-
C) possible life in non earthlike environments.
As per the information provided in the question, the microbe found in California's Lake Mono has a variation in the structure of its DNA as they use arsenic ( if phosphorous was not available) to incorporate in the nucleotides of their DNA.
This indicates the possibility of life form in non earth like environment because life forms that originated on earth like environment possess carbon, nitrogen, oxygen, and phosphorous ( that is composed of four basic elements).
But life can also be formed in an environment that lacks phosphorous ( for instance, DNA formed in microbes utilized arsenic in absence of phosphorous, indicating variation in their structure).
Thus, option C) is the right answer.