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有一批零件要加工，王师傅单独做要8小时完成，李师傅单独做要6小时完成．如果王师傅先做2小时，再由李师傅单独做，李师傅还要几小时才能完成？

答案

（1-

1
8
×2）÷
1
6
，

=

3
4
×6，

=4

1
2
（小时）；

答：李师傅还要4小时才能完成．

填空题

国家外汇管理局对个人结汇和境内个人购汇实行年度总额管理管理，年度限额为（）美元。
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单项选择题

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 longer wavelengths. Although waters of the open ocean are commonly some shade of blue, green water is commonly seen near coasts, especially in tropical or subtropical regions. This is caused by yellow pigments being mixed with blue water. Phytoplankton are one source of the yellow pigment. Other microscopic plants may color the water brown or brownish-red. Near the shore, silt or sediment in suspension can give water a brownish hue. Outflow of large rivers can often be observed many miles offshore by the coloration of suspended soil particles.Marine phytoplankton (Greek for "plant wanderers") are microscopic single-celled plants that include diatoms, dinoflagellates, coccolithophorids, green algae, and blue-green algae, among others. The growth of these organisms, which photosynthesize light, depends on a delicate balance of nutrient enrichment via vertical mixing, which is often limited by the availability of nitrogen and light. Diatoms are one-celled plants with patterned glass coverings. Each glass, or silicon dioxide box, is ornamented with species-specific designs, pits, and perforations making them popular with microscopists and, more recently, electron scanning microscopists.

What can give waters a brownish hue near the shore

A．Sediment.

B．Phytoplankton.

C．Blue pigment.

D．Diatoms.
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