填空题 For centuries, people have been enjoying the rich flavor of chocolate, a (1) made from a plant. Most people today think of chocolate as something sweet to eat or drink that can be easily found in (2) around the world. It might surprise you that chocolate was once highly treasured. Researches at the University of Pennsylvania recently (3) a study. It suggested that people in Central and South America first gathered the cacao plant much earlier and for a different use than (4) once thought. The researchers examined the (5) of substances found in ancient clay containers that were over three thousands years old. They discovered that the substance came from an alcoholic drink made from the (6) of the cacao plant. The researchers believe it was the interest in cacao as an alcoholic drink that led to the use of its bitter seeds to make what is now known as chocolate.

单项选择题 Not until most of the people had left the airport ______ his sister was there.

单项选择题 If the United States had built more homes for poor people in 1955, the housing problem now in some parts of the country ______ so serious.