Since 1970, the occurrence of malaria has increased. Why?
A. Swamplands and marshes have been drained.
B. More vaccines exist.
C. Fewer vaccines exist.
D. Malaria-carrying species of mosquitoes have become resistant to insecticides.
E. The use of insecticides in most countries has declined.
Answer: D
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Which of the following are reasons why sharks should be considered important to humans?
a. They never get cancer, and may provide information about how to prevent this disease. b. They are an important source of food c. They are a keystone species d. They never get cancer and are an important source of food e. They never get cancer and are a keystone species
A 300-W electric heater is used in a 110-V circuit. The safety fuse in the circuit can accommodate 15 A of current. How many heaters can be safely operated in the circuit?
A. 5 B. 4 C. 3 D. 2
Intermediate and felsic magmas usually arise where:a
mafic magma mixes with felsic material. b. volcanoes lie on continental margins inland of subduction zones. c. plates diverge as spreading ridges form. d. volcanoes lie above transform faults. e. mafic magma mixes with felsic material AND volcanoes lie on continental margins inland of subduction zones.
Ordinary cell thunderstorms only last about one hour and begin to dissipate when ____
A) lightning neutralizes all the electrical charge in the cloud B) all the precipitation particles in the cloud turn to ice C) the downdraft spreads throughout the cloud and cuts off the updraft D) solar heating at the ground begins to decrease