Which cells are responsible for the production of antibodies?

Which of the following organs is a primary lymphoid organ?

Which type of immunity is slow and takes time to provide an effective response?

The immunity developed by a child after an attack of measles is . . . . . . immunity.

The immune response of an elderly person becomes weak due to the degeneration of the ...... gland.

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.