【题目】This species of plant is becoming increasingly ________, so it's hard for people to find it.
A.common
B.artificial
C.attractive
D.rare

【答案】D
【解析】句意：这种植物变得越来越稀少，所以人们很难发现它。A. common“常见的”；B. artificial“人工的”；C. attractive“有吸引力的”；D. rare“稀少的”。根据“it's hard for people to find it”可知，它很稀少，故选D。