Which example below is evidence provided by living gymnosperms of an evolutionary transition between seedless and seed plants?
a) Some gymnosperms do not have reduced gametophytes.
b) The sperm of some gymnosperms have flagella.
c) In gymnosperms, two sperms are discharged into the pollen tube.
d) The sperm of gymnosperms do not require water or mobility for fertilization.
e) Gymnosperms only have one integument.