已知极限，则常数α=（)． （A)-1 （B)0 （C)1 （D)2

A vessel trawling will display a ______.

A.red light over a white light

B.green light over a white light

C.yellow light over a red light

D.white light over a green light

A.alternating red and yellow light

B.alternating white and yellow light

C.all-round white or yellow light

D.all-round white light only

______, it is widely used in making flares and fireworks.

A．as the brilliant white light that burning magnesium produces

B．Because of the brilliant white light of burning magnesium

C．The brilliant white light of burning magnesium

D．Burning magnesium produces a brilliant white light

______, it is widely used in making flares and fireworks.

A．As the brilliant white light that burning magnesium produces

B．Because of the brilliant white light of burning magnesium

C．The brilliant white light of burning magnesium

D．Burning magnesium produces a brilliant white light

A．from which

B．to which

C．at which

D．in which

Kate likes ______ clothes.

A．the light red or white

B．the light red or green

C．tile light red or purple

LEDs are different from light bulbs in that______.

A．LEDs are made up to tiny pieces of rock

B．LEDs can send out light of different colors

C．LEDs belong to incandescent lights

D．LEDs look like crystals

A vessel showing a yellow light over a white light at night is a vessel ().

A.engaged in piloting

B.towing astern

C.engaged in fishing

D.in distress

Natural light with intensity I and linear polarized light with intensity 3I both fall on a polarizer, the total transmitted intensity is 2I. What is the angle θ between the axis of polarizer and polarized direction of linear polarized light？ θ = ________°