"The percentage of Covid-19 cases and the number of deaths" is a compound subject that is plural. Therefore, it requires a plural verb. The phrase "is reflection" should be replaced with "are reflective" to ensure subject-verb agreement.
The correct phrasing is: "are reflective of the level of spread". This maintains both subject-verb agreement and the proper use of adjectives. The other options do not correctly match the plural subject or use appropriate phrasing.
The correct answer is: "are reflective of the level of spread."
Among scientists, the discovery of the double helix structure of DNA and the genetic code it incorporates is widely regarded to be one of the most significant scientific discovery of the twentieth century.