Dengue fever is caused by .

QUESTION 11:
Dengue fever is caused by a virus.
D. a virus

QUESTION 12:
A blockage in the blood flow that affects the heart's ability to work normally is known as a heart attack.
B. Heart attack

QUESTION 13:
The condition where bronchial tubes become narrowed and filled with extra mucus, causing difficulty in breathing, is called asthma.
C. Asthma

QUESTION 14:
Breathing in polluted air is an effect of air pollution.
C. Air pollution