Which technology will benefit the continent of Africa

Answer (d) may increase or decrease porosity through dissolution or deposition;

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.

Your answer would be 625,000,000.