If a substance is very sour and has a ph of 4, then you would expect the litmus paper to turn into the shade of red. A substance that is sour and has a pH level that is below 7 would indicate that the substance is an acid or has acidic properties. For an acidic solution, the litmus would be red in color. If a blue litmus paper is used, then it would turn into red while if a red litmus paper is used, then it would remain as red. There is also a general type of litmus paper where the color change range from violet to red. A litmus is widely used in distinguishing acid and bases. It can be used in liquid solutions and in gas mixtures. <span />
Answer:
d. a second exposure to an allergen
Explanation:
An autoimmune disease is a condition that occurs when the immune system attacks and destroys healthy body tissues by mistake.
Normally, white blood cells (leukocytes), produced in the bone marrow and found in the blood, help to protect the body against invasive and harmful substances known as antigens. Examples are viruses, bacteria, toxins, cancer cells, etc. Leukocytes are a fundamental part of the immune system, whose main function is to produce antibodies that keep the human body protected from the action of these antigens by destroying them.
In the case of autoimmune diseases, the immune system cannot distinguish antigens from healthy body tissues and ends up attacking and destroying normal body cells.
The causes of autoimmune diseases are not yet known, although there are many mechanisms that trigger these diseases. However, we can confirm that these diseases are not caused by a second exposure to an allergen, which is a substance that can induce a hypersensitivity reaction in some people.
Answer:

point mutation, change within a gene in which one base pair in the DNA sequence is altered. Point mutations are frequently the result of mistakes made during DNA replication, although modification of DNA, such as through exposure to X-rays or to ultraviolet radiation, also can induce point mutations
Answer:
decreased biodiversity and increased sustainability for the forest.
Answer:
maybe number one sorry if i wrong