【单选题】

The giant pandas’ prospects are better now than in the recent past. New insights into behavior, diet and physiology offer hope that we may be able to protect and breed these animals more effectively.

Pandas are exceedingly elusive. Pandas are natural vagrants, unsociable and eccentriC、There has been considerable debate over the evolution of pandas. Some experts have thought that they descended from raccoons. Others believe they share a common ancestor with the bear, but evolved independently.
The animals could once be found in much of southern and easternChina, as well as parts of SoutheastAsiA、And though the panda’s range has steadily shrunk, its habits are unaltereD、The panda’s routine is indeed a bum’s life, spent wandering from one bad meal to another and bedding down in the nearest dark corner.Although pandas can swim and climb trees, they spend most of their time seeking out and chewing bamboo.
Pandas have been known to eat chicken and honey when bamboo is in short supply.But in the wild, bamboo is their primary fare.And because it is such a poor source of nutrition and hard for them to digest, pandas must eat prodigious amounts. Pandas consume about 30 pounds of bamboo a day. On this monotonous diet, they attain weights of up to 250 pounds.
They make a variety of sounds: bleating, chirping, huffing, snorting and even barking like a dog if startleD、At about age five, the female, smaller than the male, will moan, signaling she is receptive. Her call is often answered by as many as three or four males.
In lateAugust or September, after a gestation period estimated at 90 to 160 days, the female gives birth. Her litter often consists of two mouse-size newborns covered in sparse white hair, through which their pink skin shows.But she is likely to focus on a single cub--not necessarily the healthier-- and let the other die. The baby is cared for in a cave or hollow tree that the female has lined with bamboo twigs. The mother assumes sole responsibility for the cub, nursing it often during the first six months. She guards her infant closely, earning it in her paw or teeth. Not until it is 18 months old is her offspring, by then almost 100 pounds heavier, ready to live on its own.
A、female can conceive only two or three days a year.Because she takes 18 months to rear her offspring, she will reproduce only once every two years.
The most promising hope for the panda’s future seems to be the increased efforts by theChinese government. Public concern for the welfare of pandas has been heightened by stiff penalties for poaching.
So we can, perhaps, begin to dream again of a future with the pandas, born in the wild or returned there after birth, full-furred giants wandering and occasionally meeting deep in the verdant tangles of bamboo. We may never see them, but it is rewarding to think the pandas will be there, for these captivating creatures clearly hold a special place in our hearts.
The underlined word "receptive" (Line 2, ParA、5) means______.
A、femaleB、popularC、mature D、startled