Aquatic biomes cover approximately three-quarters of Earth's surface. Examples of aquatic biomes include lakes, streams and rivers, wetlands, estuaries, and oceans. Different types of aquatic biomes are distinguished by their physical and chemical characteristics, their depth, and, for some biomes, their distance from shore. Many temperate lakes undergo semiannual turnover, a process that mixes the surface and bottom waters, resulting in the redistribution of oxygen and nutrients.
Aquatic biomes can be distinguished by chemical characteristics such as dissolved oxygen content and salinity and by physical characteristics such as water flow.
Which five of the following statements about aquatic biomes are true?

a. The lowest levels of dissolved oxygen in a stream are generally found in its turbulent headwaters.
b. Wetlands have slow water movement or no water movement and no turnover.
c. Tropical coral reefs generally exist in relatively shallow areas of the ocean.
d. Estuaries are very productive and are used as breeding grounds by many species of fish.
e. A freshwater organism permanently attached to the substrate would be unlikely to survive and reproduce in an estuary.
f. Temperature drives water movement in some lakes.
g. All wetlands have soils that dry out periodically.

Covalent bond is the correct answer

Science27 of the most iconic, jaw-dropping photos of the earth and the moon from spacedave mosher  oct 1, 2018, 11: 13 am etnasa/flickrapollo 11 astronauts took this photo of earth on july 20, 1969.from the ground, earth looks like a boundless fertile plain that beckons to be explored and exploited.but astronauts would beg -  and even plead  - to differ."you realize that people often say, 'i hope to go to heaven when i die,'" jim lovell, an astronaut who flew on the apollo 8 and apollo 13 missions to the moon, previously  told business insider. "in reality, if you think about it, you go to heaven when you're born."lovell has seen first-hand that we live on a tiny rock hopelessly lost in the void. he's also quick to tell you it's the only one we've got - a  fragile spaceship  for more than 7 billion people: "you arrive on a planet that has the proper mass, has the gravity to contain water and an atmosphere, which are the very essentials for life. and you arrive on this planet that's orbiting a star just at the right distance - not too far to be too cold, or too close to be too hot - and just at the right distance to absorb that star's energy and then, with that energy, cause life to evolve here in the first place. in reality, you know, god has really given us a stage, just looking at where we were around the moon, a stage on which we perform. and how that play turns out is up to us, i guess."humanity has recorded photos of earth from hundreds, thousands, millions, and even billions of miles away, some of them taken by lovell himself.these images not only scientists study our dynamic world, but also understand how a habitable planet looks from afar, which aids the search for  more worlds. most importantly, however, the images underscore our peculiar existence on  a mote of cosmic dust.take a moment to ponder 27 of the most arresting images of earth that humankind has ever captured from space.a

C) they are specialized meaning they are designed to do different things