The new car won’t go into production soon. The engine of it hasn’t been fully ___.

A．carried out

B．worked out

C．tested out

D．put out

下列自然特征中，本身就包含着荒漠化潜在威胁的是

A．干旱的气候条件

B．高原、盆地为主的地形

C．人口激增

D．过度放牧