How can you tell if a article is secondary source or primary source

What element is able to combine with itself and hydrogen to form large molecules ?

Drag each description to the correct location on the image. not all descriptions will be used. describe the parts of a comet. the frozen part of the comet the atmosphere of gases and dust formed when the nucleus vaporizes tail made of small, solid dust particles tail made of ions that appears to point away from the comet's orbit

Which of the following molecules can be broken down into simple sugars? a. nucleic acid b. protein c. lipid d. carbohydrate