※46～48                     Rare Blue Moon for Halloween        Have you heard of the saying "once in a blue moon"?It means something almost never happens. Usually, we only seeone full moon each month. When there are two full moons in onemonth, that is called a "blue moon”. And next month, we will seea "blue moon" in the night sky.             Experts say October will have two full moons. The firstwill happen on October 2nd, at 5am. The second will come onOctober 31st, 10pm. That night is also Halloween night. Theexperts say if the weather is clear, and there aren't too manyclouds in the sky, you will be able to see the "blue moon".       Scientists say there are usually 29.5 days between everyfull moon. And blue moons only happen once every two to threeyears. Even though it is called a "blue moon", the moon doesn'tactually turn blue. It is still just a grey-white color. But, scientistssay if the air is full of dust or smoke, the moon could actuallylook blue. This can happen because of big forest fires orvolcanoes erupting.        In 1883, a volcano called Krakatoa in Indonesia erupted.The eruption was so big that people in Australia heard it.More than 36,000 people were killed. The eruption filled the airwith so much dust and smoke, that the moon looked blue foralmost two years after.       It’s such a good chance to see a “blue moon” onHalloween. Remember to invite your family and friends to gotrick-or treating and enjoy the sight together.                                                            Adapted from ICRT News Lunchbox

 * rare 稀少的 expert 專家 dust 灰塵volcano 火山 erupt 爆發
【題組】46. How often can we see a “blue moon”？
(A) It’s rare to see one, maybe once in a lifetime.
(B) Almost two years after the eruption of a volcano.
(C) Every two to three years.
(D) 29.5 days between every full moon.