17. catalyst is (a) a molecule or atom which increases the rate of reaction (b) a molecule or atom which decreases the rate of reaction (c) a molecule or atom which alters the rate of reaction but does not take part in the chemical reaction (d) both a and b

under a microscope, cancer cells may look very different from normal cells. they often have different sizes and some may be larger than normal while others are smaller. cancer cells are often abnormally shaped and the control centre of the cell (the nucleus) may have an abnormal appearance.

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