To determine the best estimate for the number of COVID-19 cases in the UK on day 20 using the graph, we need to look at the corresponding point on the y-axis for day 20 on the x-axis. Since I can't view the image, if you have the graph data points labeled, please check the y-value at x = 20.
From the options provided, if there is a point near 2,000 cases, 10,000 cases, 12,000 cases, or 15,000 cases on the graph at day 20, choose the one that most accurately reflects that point.
Please consult the graph to find the exact coordinate and match it with the options listed. If there’s any more specific information or data from the graph, feel free to share it to narrow down the choice!