About which of the following do Leibniz and Spinoza disagree?
(a) There cannot be two substances of the same nature.
(b) Every substance necessarily exists.
(c) Each thing has a conatus by which it strives to continue in its own nature.
(d) Nothing ever tends, by its own nature, to cease existing.
(e) Whatever happens in a body is reflected in its mind, and vice versa.
(f) None of the above.