Lymphoid organs limit the spread of disease by filtering and trapping microscopic pathogens, preventing them from traveling elsewhere in the body. Which of the following statements correctly links a functional or structural feature with the appropriate lymphoid organ?A) The outer cortex of the thymus consists of lymphoid follicles separated by inward extensions of the capsule called trabeculae.
B) Red pulp, found in the spleen, contains macrophages that destroy old erythrocytes.
C) White pulp in the lymph nodes contains macrophages and leukocytes that filter pathogens from lymph.
D) The lymph nodes secrete hormones that produce functional T cells, which protect the body from pathogens.

You haven't provided the chart of birds nor a short description of it, but I can give you a general guide dealing with the use of a Dichotomous Key.

As you mentioned, a Dichotomous Key is a tool that allows the identification of organisms or objects, based on their morphological characteristics. For birds, there are some important features that can be useful to classify them into groups: size, beak shape, eyes, feet shape, feathers, tail form, primary colours, etc.

One of the first steps for starting a bird dichotomous key could be identify the birds location, but if you don't have this infomation, then classify them by size, going from very small to very large. If you don't have the size information, you can begin by classifying them by shape (pigeon-like, duck-like, owl-like, etc.). Other basic and useful way of classifying birds in a Dichotmous key is by beak shape (cone, needle, curved, etc.).

Explanation:

The best way to start a Dichotomous Key is going from general characteristics to more detailed ones. That's the reason why location could be an interesting first step, taking in account that bird's location is very important. Their shape, size and beak are also general features that you can notice just by looking at a bird chart, and could be a good first step to classify them into groups.