Question

Which of the following was one of the earliest changes thatcontributed to the success of plants transitioning from aquatic toterrestrial ecosystems?
a. The ingestion of photosynthetic bacteria, enabling plants tophotosynthesize
b. The development of vessels to transport water
c. The development of roots to obtain nutrients and water fromsoil
d. Spores or zygotes encased in a tough coat to resist dryingout
e. The development of flowers to attractpollinator

Is it B or D? I would assume D is the seed of a gymnosperm.According to the info below, that came after the evolution ofvessels to transport water.

Please explain your answer

http://www.clas.ufl.edu/users/pciesiel/gly3150/plant.html

• The oldest fossils reveal evolution of non-vascular plants bythe middle to late Ordovician Period (~450-440 m.y.a.) on the basisof fossil spores.
• These first non-vascular, "amphibious" plants, were limitedprimarily to lowland, wet areas, of temperate to tropicallatitudes. Still most land areas were barren.
• By some 420 m.y.a., seedless vascular plants evolved which werebigger and more diverse than their ancestors. These seedlessvascular plants required water for sperm to reach the eggs and werestill limited in their distribution to wet climates. These seedlessplants grew to tree size, reaching 10 or more meters by the lateDevonian (~370 m.y.a.). Lowland swampy environments had abundantseedless plants.
• After the 1st land plants evolved (approximately 450 m.y.a.)they underwent rapid expansion and radiation with great forests byMiddle DevonianPeriod. (385 m.y.a.). Although these forests were limited in theirextent, vast quantities of organic material were deposited andpreserved in swampy environments. Through time and burial, thisorganic material was converted to coal, forming the firstsignificant coal deposits of Earth history.
• At a similar time (late Devonian, ~375-360 m.y.a.), seedbearing gymnosperm plants (non-flowering) evolved. The developmentof the seed allowed plants to proliferate and spread to drier areasof continents. Gymnosperms became the dominant plant type between~290 to 145 m.y.a. and are still common today.
• During the final days of the dinosaurs (Cretaceous), the finalchapter of plant evolution began. This was the evolution offlowering plants (angiosperms). During the Cretaceous Period,angiosperms began overcoming non-flowering plants as the dominantland plants. Since this time they have become the dominant landplants.