We do not know exactly how many whales there are in the sea because we can't count them. But we believe at the beginning of the eighteenth century there were 105,000 humpback whales and 120,000 right whales. At the beginning of the twentieth century there were 75,000 humpbacks and 80,000 rights. Since 1900 their numbers have fallen very quickly. Between 1935 and 1950 the number of humpbacks fell from 20,000 to 10,000 and since 1950 the number has fallen to only 6,000. The number of right whales has fallen even faster. In 1935 there were 25,000. The number fell to 6,000 in 1950 and since 1950 the number has fallen to 4,000. Men have always been hunters. Thousands of whales have become victims . It's time to do something to protect whales. The passage is mainly about   _  .
the number of humpback whales the number of right whales hunting whales the necessity of protecting whales