Which of the following are the incorrect statements about 'Keystone species'.
1. Keystone species are the small-sized plants and organisms which have large effect on the environment.
2. Keystone species play critical role in maintaining the structure of an ecological community.
3. Keystone species do not generally affect other organisms.
(a) 1 and 2
(b) 2 and 3
(c) 1 and 3
(d) All are correct