TOEFL Listening: TPO-TOEFL阅读TPO - YCD5C4182Y43725SN$

According to paragraph 2, a major reason why natural salt marshes are so productive is that they are A. inhabited by long-lived seaweed and marsh grasses that reproduce gradually B. kept clear of excess plant material by the tides C. regularly supplied with high levels of nutrients D. home to a wide variety of different species of grasses