One of the most important positive land modifications made in china was to a. improve transportation methods using the land b. create more farms for cash crops on the land c. reforest regions to preserve the land d. build more cities on the land

C. Reforest regions to preserve the land

Explanation:

China is a country that doesn't really have a good reputation when it comes to preserving the environment. This largely because of its eastern part where the industry and population are the most concentrated, so the pollution is enormous, and the environment has suffered greatly.

China though is also a country that has made big efforts in preservation of the land, transforming it positive manner, and helping the environment in the process, as well as the human population. This has been done with reforestation and greenification of land that has been stripped of its vegetation, or land that has been semi-arid or arid.

This has resulted in large portions of land, specially in the northern and western part of the country, the deserts to be converted into land covered with forests, shrubs, grasses. This is helping the environment, the human population, and fights the pollution and desertification.

cirrus clouds: lacy or wispy clouds that form at high altitudes it would generally happen before a change in the weather.

81 is a composite number.