The phenomenon of single or double fertilization is unique to the seed plants

Double fertilization

Explanation:

The phenomenon of double fertilization is unique to flowering plants (i.e., angiosperms). Each pollen grain produces two male gametes (sperm cells), one of which fertilizes the egg to form the zygote, whereas the other sperm fuses with polar nuclei in the female gametophyte in order to form a triploid cell (3n) called endosperm. Subsequently, this endosperm will support embryonic growth by supplying storage nutrients and by serving as a mechanical barrier during seed development and germination.

one of the most common forms of pain or discomfort we feel during strenuous exercise is a burning sensation in our lungs or muscles that goes away shortly after we cease the activity. this is caused by a build-up of lactic acid.

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explanation: