Questions 63-68 are based on the following passage.
The blue of the sea is caused by the scattering of sunlight by tiny particles suspended in the water.Blue light, being of short wavelength, is scattered more efficiently than light of longerwavelengths. Although waters of the open ocean are commonly some shade of blue, green water iscommonly seen near coasts, especially in tropical or subtropical regions. This is caused by yellowpigments being mixed with blue water. Phytoplankton are one source of the yellow pigment. Othermicroscopic plants may color the water brown or brownish-red. Near the shore, silt or sediment insuspension can give water a brownish hue. Outflow of large rivers can often be observed manymiles offshore by the coloration of suspended soil particles.
Marine phytoplankton (Greek for “plant wanderers”) are microscopic single-celled plants thatinclude diatoms, dinoflagellates, coccolithophorids, green algae, and blue-green algae, amongothers. The growth of these organisms, which photosynthesize light, depends on a delicate balanceof nutrient enrichment via vertical mixing, which is often limited by the availability of nitrogenand light. Diatoms are one-celled plants with patterned glass coverings. Each glass, or silicondioxide box, is ornamented with species-specific designs, pits, and perforations making thempopular with microscopists and, more recently, electron scanning microscopists.
64. Phytoplankton are the source of which color pigment?
A. Red.
B. Green.
C. Yellow.
D. Blue.
65. What can give waters a brownish hue near the shore?
A. Sediment.
B. Phytoplankton.
C. Blue pigment.
D. Diatoms.
66. Which of the following is not a type of phytoplankton?
A. Green algae.
B. Diatoms.
C. Blue-green algae.
D. Amoeba.
67. The growth of phytoplankton is often limited by the availability of .
A. oxygen
B. hydrogen
C. nitrogen
D. carbon dioxide
68. The main idea of this passage is that .
A. light causes sea color
B. sea coloration is varied because of a combination of length of light waves and microscopic plant life and silt
C. microscopic plant life causes sea color
D. water composition causes sea color