Correct Answer: (b) last year found that
Solution:The most appropriate option to substitute the underlined segment in the given sentence would be- last year found that. A major report last year found that one in four species is at risk. Past tense of "find" is "found" (to discover, see, or get something you have been searching for) while 'Founded' is past and past participle of 'found' which means to establish something.
Hence, the correct answer is option (b).