An extremely rare occurrence in humans is a multiple pregnancy with the embryos at different stages due to fertilization weeks apart. What mechanism normally prevents this from happening?
A. The embryo's secretion of FSH and LH maintains the corpus luteum, keeping estradiol and progesterone high until the placenta takes over secretion of these hormones.
B. The embryo's secretion of GnRH maintains the corpus luteum, keeping FSH and LH high until the placenta takes over secretion of these hormones.
C. The embryo's secretion of hCG maintains the corpus luteum, keeping estradiol and progesterone high until the placenta takes over secretion of these hormones.
D. The follicle's secretion of polar bodies maintains the fimbriae, keeping estradiol and progesterone high until the fallopian tube takes over secretion of these hormones.
C. The embryo's secretion of hCG maintains the corpus luteum, keeping estradiol and progesterone high until the placenta takes over secretion of these hormones.
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Following their respective breeding seasons, several species of hummingbirds occur at the same locations in North America and several hummingbird flowers bloom simultaneously in these habitats. These flowers seem to have converged to a common morphology and color. Birds have the most visual sensitivity to the color red. Following their breeding season, these species of hummingbirds are
A. allopatric. B. sympatric.
Maria has been in labor for 12 hours, and her obstetrician thinks that it is time to artificially induce birth. What hormone will the physician inject?
A) estrogen B) vasopressin C) prolactin D) oxytocin
Rhizomes that end in enlarged structures that are specialized for storage are called
A) bulbs. B) tubers. C) taproots. D) runners.
Which of the following is a microbial product used to reduce crop damage?
A) Bt toxin B) saxitoxin C) ice-minus D) both Bt toxin and ice-minus E) both Bt toxin and saxitoxin