So because Brazil is #1 in sugar export, no other country has greater than it's 21% of the worldshare. 25% is 1/4th of the world share, so since Brazil is number 1, no other country can produce 25%. Answer is yes.
For the second answer, find all world producers that are <20, of which there are 5. The first, beef, is produced at 16%, which is les than 20, but Brazil is the number 1 exporter of that. That contradicts the statement, so this is No.
For three, again No, along similar lines to 2.