What is the important of ozone layer to man?
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5×^2+20-15 or -(5x^2-20+15)

Well, a and b together would be negative. b alone would also be negative.

When a lake, river or other aquatic  system  becomes  eutrophic, it can have serious negative effects on other organisms like fish, birds and even people.if an algal bloom is so bad that it causes wide-spread death  in  the  water, the organisms that die will all sink to the bottom and start to decompose.

Although nelson mandela was arrested for treason and sentenced to life in prison, he was not arrested in 1964. he was arrested in 1962. therefore, letter b is false.