如图，半圆的直径AB=6，O为圆心，C为半圆上不同于A、B的任意一点，若P为半径OC上的动点，则 $\left(\overrightarrow{PA}+\overrightarrow{PB}\right)·\overrightarrow{PC}$的最小值为（　　）

日常生活中的许多现象都与化学反应有关，下列现象与氧化还原反应无关的是（  ）。

    High in thick bamboo forests in the misty, ____ (rain) mountains of southwestern China ____ (live) one of the world's rarest mammals: the giant panda, also called the panda, Only about 1,000 of these black-and-white ____ (relative) of bears survive in the wild.

    Pandas eat almost nothing ____ bamboo shoots and leaves. ____ (occasion) they eat other plants, fish, or small animals, but bamboo accounts for 99% of their diets.

    Pandas eat fast; they eat ____ lot, and they spend about 12 hours a day ____ (do) it. The reason is ____ they digest only about a fifth of what they eat. Overall, bamboo is not very nutritious. To stay healthy, they have to eat a lot-up to 15 percent of their body weight in 12 hours-so they eat fast.

    Pandas' molars(臼齿) are very broad and flat. The shape of these teeth helps the animals crush the bamboo shoots, leaves, and stems they eat to get the bamboo to their mouths, ____ hold the stems with their front claws, which have enlarged wrist bones that act as thumbs for grasping things. A panda should have at least two bamboo species where it lives, or it will starve. Pandas are shy; they don't go into areas ____ people live. This restricts pandas to very limited areas.