In 2017, Shanna Swan and Hagai Levine, along with six other researchers, estimated the average sperm count for 43,000 men in 55 countries across the world. The data, from 185 previously published studies, suggest that sperm counts fell by about 25% between 1973 and 2011. They found that sperm counts had in fact fallen by about 50% in Western countries over the period. Although the data were less plentiful, similar trends were observed in developing countries, too.
Please have a look at the chart below and discuss what you see with your teacher.