What is double fertilization (双受精)？And what is the biological significance （生物学意义） of double fertilization?

in vitro fertilization是指体外受精。（ ）

中国大学MOOC: what is in vitro fertilization?

what is in vitro fertilization? A: 体外受精 B: 胚胎培养 C: 受孕 D: 试管婴儿

‍人工授精的英文是（ ）。‌ A: mating B: breeding C: artificial insemination D: fertilization

What are the three ways plants bear fruits? A: Double fertilization B: Parthenocarpy C: Apomixis D: Pollination

Why do plants spread their fruits or seeds? A: For pollination B: For rooting C: For fertilization D: For offsprings growing better

Which of the following is wrong about the development of fertilized eggs? A: Zona pellucida reaction ensures single egg fertilization B: Egg swims in the fallopian tube and divides twice a day C: Egg moves in the fallopian tube and divides with its volume increasing D: Fertilized egg runs in the fallopian tube for 72 hours E: On the 4th day after fertilization, morula enters the uterine cavity

Insect reproduction may be characterized by all of the following EXCEPT: ( ). A: direct sperm transfer B: copulatory organs C: indirect fertilization D: an ovipositor of the female E: sperm storage in the sperm receptacle

Most of the X-lined genes in humans are expressed in equal amounts between males and females because A: only one of the two X chromosomes is active in each cell in the females. B: X-linked genes on the X chromosome in males are expressed two-fold higher than in females. C: only one X chromosome is kept after fertilization. D: Half of the RNA transcripts from X chromosomes in female cells are degraded after transcription.