Which of the following was an effective strategy in controlling the COVID-19 pandemic?

a. Widespread testing available at both traditional healthcare settings (e.g., hospitals, urgent care centers) and nontraditional venues (e.g., supermarkets, walk-in and drive-through centers)
b. Mass testing of individuals at the community level regardless of whether symptoms were present
c. Testing, contact tracing, and isolation of positive cases
d. All of the above