Algae is a primitive form of life, a single-celled or simple multiple-celled organism that is able to conduct the process of photosynthesis. It is generally found in water but can also be found elsewhere, growing on such surfaces as rocks or trees. The various types of algae are classified according to pigment.

Blue-green algae, or Cyanophyta, can grow at very high temperatures and under high- intensity light. This type of algae is the oldest form of life with photosynthetic capabilities. Fossilized remains of blue-green algae more than 3.4 billion years old have been found in parts of Africa.

Green algae, or Chlorophyta, is generally found in fresh water. It reproduces on the surfaces of enclosed bodies of water such as ponds or lakes and has the appearance of a fuzzy green coating on the surface of the water.

Brown algae, or Phaeophyta, grows in shallow, temperate water. This type of algae is the largest in size and is most recognizable as a type of seaweed. Its long stalks can be enmeshed on the ocean floor, or it can float freely on the ocean's surface.

Red algae, or Rhodophyta, is a small, delicate organism found in the deep waters of the subtropics. This type of algae has an essential role in the formation of coral reefs: it secretes lime from the seawater to foster the formation of limestone deposits.

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions

What is the author's main purpose?

Câu hỏi liên quan

• Which of the following business schools has NOT shown a decrease in enrollment?

• The word “threat” in paragraph 2 could best be replaced by ___________.

• Which of the following is NOT mentioned in paragraph 1 as resulting from repid ecological change?

ZUNIA12

• Which of the following is NOT mentioned as an activity of relaxation in the countryside of Britain?

• The word “forces” in line 9 could best be replaced by:

• The word "ball" in paragraph 2 probably means ...............

• The word “basis” in paragraph 1 is closest in meaning to_________.

• What did the five campers do when they saw a group of apelike creatures?

• The word “contagious” is closest in meaning to ___________.

• What is the ozone layer made of?

• What is the setting of Tolkien's trilogy?

• Why does the author mention “long, grueling hours without sleeps” in paragraph 4?

• According to the passage, an exuberant tone of voice may be an indication of a person's _______.

• A nod of the head from the teacher will likely ask his student to __________ what he is saying.

• The changes possibly caused by the cellphones are mainly concerned with ______.

• Which of the following statements is NOT true?

• Nowadays there are ____________.

• According to the author, M.L. _______.

• According to the passage, what does a constricted and harsh voice indicate?

• How many Americans are involved in telecommuting?