Complete the text with the words given below.

Hay fever is a seasonal allergy to pollens; the term hay fever, however, is less than ... description since an attack can be brought on by ... other than hay-producing grasses. Hay fever is generally caused by ... pollens, particularly ragweed pollen. The amount of pollen in the air is largely ... on geographical location, weather, and season. In the eastern ... of the United States, for example, there are generally three periods when ... from various sources can cause ... hay fever suffering: in the springtime months of March and April when pollen from trees ... the air, in the summer months of June and July when grass pollen fills the air, and at the end of August when ... pollen is at its most concentrated ... .