单项选择题

Australian aborigines have (31) the continent for over 45,000 years. Aboriginal people living in one place differ significantly from those in (32) parts of Australia in dietary habits.
The life of the desert aborigines is one of (33) movement from one water-hole to the next and they (34) remain in any one place for more than a few days. The women quickly exhaust the supplies of grass seeds, yam and fruits within (35) distance of the water supply, and the hunting activities of the men quickly (36) the game to other places.
The northern fringes of the continent are especially rich (37) food. The seas supply people with marine (38) of countless kinds—fish and turtles (39) the aborigines capture by fishing, or spearing with a harpoon. (40) there is also a wide (41) of foods available to those aborigines who live in the forest country, far from the sea and swamps. In this habitat many creatures are to be caught, fruits (42) plucked from the trees, and tubers to be dug from the ground.
For the native people who live on the sea-coast or the swamplands, the nesting season, (43) , is a time of (44) The (45) of their eggs provide the native people with an abundant supply of easily gathered food. People cook the eggs in the hot sand of the camp-fire, and they (46) them when they are almost ready to hatch, believing, quite correctly, that they are much more satisfying in this state (47) when they are newly (48) . The eggs of the emus are another source of food, two of them, especially if they are (49) incubation, (50) sufficient for a meal.