Mark the correct statement about the loss of biodiversity.

The number of species currently existing can only be estimated but not the exact number of species that are extinct.. Nature’s biological library is burning even before we
catalogued the titles of all the books stocked there. Large fraction of species faces the threat of becoming extinct even before their discovery. The extinction rate is high and that human activities threaten Earth’s biodiversity at all levels. The current species extinction rates are estimated to be 100 to 1,000 times faster than in the pre-human times approximately. Human activities are responsible for the faster rates. There were five episodes of mass extinctions in the past and the current one is the sixth extinction.