How has man negatively impacted the tundra biome

They have contributed to heating up the environment 

One of the biggest threats to the tundra is global warming. As fossil fuels burn elsewhere on the planet, the atmosphere warms in all locations. This causes melting of permafrost, resulting in the collapse of tundra ecosystems. As permafrost melts, it allows frozen plant material to decay, releasing more carbon dioxide and accelerating global warming, according to Marietta College

C. a mature ovule of a plant.

Then it is june the conclusion to the second sentence is just restating "if it is june then it is summer"