Sustainable development is long-term which focuses on the environment and natural resources.
A. plan; preserve
B. plan; preserving
C. planning; preserving
D. planning ;preserve
网友回答
A. plan; preserve
B. plan; preserving
(答案→)C. planning; preserving
D. planning ;preserve
解析：考查名词及动词。plan计划；planning n. 规划,计划,设计。focus on doing集中做，根据句意选C。