In the following passage some words have been deleted. Fill in the blanks with the help of the alternatives given. Select the most appropriate option for each blank.

China is the largest producer of pork, but it (1) ______ a big problem at the moment. There is an epidemic (2) _____ is killing its pigs. The virus was first (3) _____ in August last year, but one million pigs have died by now. It is a (4) ______ virus and when a pig catches it, it dies. China thinks that one third of (5) ______ pigs are going to die by the end of this year.

Q:

Select the most appropriate option for blank No. 3.

• 1
  discovered
• 2
  searched
• 3
  learned
• 4
  invented