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Hai nguyên tử X kết hợp với một nguyên tử O tạo ra phân tử oxit. Trong phân tử, nguyên tử Oxi chiếm 25,8% về khối lượng . Hỏi nguyên tố X là nguyên tố nào sau đây A. Na B. Li C. K D. Ca
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Messages from the Stone Age The incredible pre-historic Chauvet cave art in France is painted in (0) ........ colours and dates back to a period around thirty thousand years ago when early humans first started to create rock art. Although various (1) .... .. .. of this art have been found in caves in Western Europe, very few people have seen the art at Chauvet because it is located (2) .... .. .. inside an inaccessible underground cave system. Those who have seen it say that it is very impressive, showing animals (3) ........ horses, rhinos and I cows, and that the artwork is good enough to (4) .. ...... modern compositions. The first scientists to (5) ........ the Chauvet paintings missed some other important (6) ...... .. however. The walls of the cave are also marked with a series of lines and symbols, that were initially (7) ..... ... as insignificant. But recent research has suggested that these marks may represent humankind's first steps towards the development of writing, which is (8) ........ people to rethink their ideas about when written communication first started. 1 A illustrations B models C cases 0 examples 2 A deep B thick C long 0 dense 3 A by means of B apart from C as well as 0 such as 4 A rival B compare C compete 0 oppose 5 A arrive B reach C meet 0 know 6 A instances B matters C details 0 issues 7 A believed B regarded C thought 0 agreed 8 A resulting B having C making 0 causing

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