Antarctic __________ we know very little is covered with thi

选D.
翻译：我们（对其）知之甚少的南极洲常年冰雪皑皑.
说明：（限制性）定语从句,修饰限定主句的主语Antarctic（南极洲）,主句为主系表结构；可拆句处理——
1.We know very little about Antarctic.我们对南极洲知之甚少.
2.Antarctic is covered with thick ice all the year round.南极洲常年冰雪皑皑.
然后合二为一,用句2里的主语取代句1里的宾语.
A、B、C均缺介词（know about Antarctic）,可排除.

D
我们知之甚少的南极洲终年被冰雪覆盖。