Câu hỏi:

Read the following passage and mark the letter A, B, C or D on you answer sheet to indicate the correct answer to each of the questions. 

     Do you like tuna? People in many countries like to eat tuna whether it is canned, cooked, or raw. Unfortunately, humans are now eating too much tuna, and some species are becoming rare.

     The name “tuna” refers to over 48 species of carnivorous fish that live in Pacific, Atlantic, Indian, and Mediterranean oceans. The most important commercial species of tuna are yellowfin, bluefin, bigeye, albacore, and skipjack. Skipjack makes up the majority of canned tuna, while the other species are served either raw or cooked. 

     While the fishing of skipjack tuna is currently sustainable, it is widely accepted that the other species have been severely overfished. In particular, bluefin tuna stocks are now at risk of collapse. From 1976 to 2006, the population of bluefin decreased by 92%. Overfishing continues despite repeated warnings. In 2009, scientists recommended that the quota for northern bluefin tuna be set at 7,500 tonnes, but the Atlantic Tuna Commision set it at 16,000 tonnes. Even this limit was ignored, with the total catch of Atlantic bluefin estimated to be 60,000 tonnes in 2009. 

     The reason for this over-fishing is that yellowfin, bluefin, and bigeye tuna are prized for use as sashimi (raw fish). This makes them very valuable. In 2011, a bluefin tuna weighing 342 kilograms was sold in Tokyo for 32,49 million yen (USD 396,000). Recently, the sashimi-tuna species have become so rare, and their price is so high that many sashimi restaurants have had to close.

     In response to decreasing tuna stocks, scientists have been trying to breed tuna in captivity. In 2009, an Austrian company succeeded in breeding southern bluefin tuna in land-based tanks. This is an important development because tuna farming currently relies on raising juvenile tuna that are caught in the wild.  Catching these juvenile tuna makes overfishing even worse. 

          Everyone needs to work together to help the wild tuna survive. You can help to save the wild tuna, too.  Next time you have tuna, check to make sure you aren’t eating a wild bluefin, yellowfin, or bigeye. Hopefully, if we all play our part, it won’t be too long before stocks of tuna recover to their former levels

The word "This" in the 5th paragraph refers to _________.