Which terminal end of the antibody protein structure is responsible for binding with the antigen?

Which of the following requires the injection of preformed antibodies or antitoxins into the body to provide immunity?

What does the indicated part in the given figure represent?

Fill in the blanks: Our body, when it encounters a pathogen for the first time, produces a response called . . . . . . $a$ . . . . . . response, which is of . . . . . . $b$ . . . . . . intensity. Subsequent encounters with the same pathogen elicit a . . . . . . $c$ . . . . . . intensified . . . . . . $d$ . . . . . . response.

What are antigens composed of?

Interferons are synthesized in response to which of the following?