You are presented with a paragraph from a COVID-19 literature. Classify the topics of this piece of text by choosing from the following categories:

- Epidemic Forecasting: The content relates to predictions about the spread of COVID-19.
- Treatment: The paragraph discusses therapeutic methods or medication for COVID-19.
- Prevention: The content covers measures to prevent the spread of COVID-19.
- Mechanism: The paragraph explains the biological mechanisms of the virus.
- Case Report: The content is a report of a COVID-19 case.
- Transmission: The paragraph discusses how COVID-19 is transmitted.
- Diagnosis: The content is about diagnosing COVID-19 in individuals.

Your classification should be provided as an element within a JSON array. The array should be formatted with topics enclosed in double quotes and separated by commas, following the JSON format, for example: ["Topic1", "Topic2", ...]. Include all applicable topics within the array. Your output should be a valid JSON array, and no additional text should be included in your response.

Article:

As a kind of human betacoronavirus, SARS-CoV-2 has endangered globally public health. As of January 2021, the virus had resulted in 2,209,195 deaths. By studying the evolution trend and characteristics of 265 SARS-CoV-2 strains in the United States from January to March, it is found that the strains can be divided into six clades, USA clade-1, USA clade-2, USA clade-3, USA clade-4, USA clade-5, and USA clade-6, in which US clade-1 may be the most ancestral clade, USA clade-2 is an interim clade of USA clade-1 and USA clade-3, the other three clades have similar codon usage pattern, while USA clade-6 is the newest and most adaptable clade. Mismatch analysis and protein alignment showed that the evolution of the clades arises from some special mutations in viral proteins, which may help the strain to invade, replicate, transcribe and so on. Compared with previous research and classifications, we suggest that clade O in GISAID should not be an independent clade and Wuhan-Hu-1 (EPI_ISL_402125) should not be an ancestral reference sequence. Our study decoded the evolutionary dynamic of SARS-CoV-2 in the early stage from the United States, which give some clues to infer the current evolution trend of SARS-CoV-2 and study the function of viral mutational protein.
["Mechanism"]