Select the most appropriate set of options to fill in the blanks. Mexico is home to more species of oak than any country in the world, though many of them are(1) . In the case of the arroyo oak, as it is known, the species now faces a particularly(2) problem. Though plenty of trees aged more than 100 years can be found, locals(3) that in recent years there had been no seedlings that have sprouted from their acorns in sight. For some reason, the trees had(4) stopped reproducing. (Sentence Completion) Blank 1 A. threaten B. threatened C. threatens D. threatening. Blank 2 A. struggling B. troubling C. grieving D. agitating Blank 3 A. regarded B. recognized C. noticed D. caught Blank 4 A. commonly B. directly C. easily D. simply