The characteristics of swallows are as follows: Swallows belong to passeriformes 1 genus. This genus of birds is small, with a body length of 130 to 180 mm, a long wing tip and a forked tail. Most of the feathers on the back are blue-black, so they were called mysterious birds in ancient times. The wing tip is long and good at flying, the mouth is short and weak, and the mouth is wide, which is a typical mouth shape of insect-eating birds.

Short feet and strong claws. There are 20 species in the world and 4 species in China, among which domestic swallow and Jin Yan are more common. Swallows are chestnut red in the front waist, with irregular horizontal bands in the back chest and milky white in the abdomen. Swallows usually breed from April to July. Domestic swallows nest under the eaves of farmhouses. The nest is made of saliva bonded with soil and grass stalks, covered with soft weeds, feathers, rags and so on. And some Artemisia annua leaves.

The nests are dish-shaped and breed 2 nests every year, mostly from May to early June and from mid-June to July, and each nest lays 4 to 6 eggs. The second nest is less, 2 to 5, with milky white eggs and hermaphroditic eggs hatching.

Characteristics of expository writing

The primary feature of expository writing is knowledge, that is, it focuses on explaining and spreading some recognized knowledge, rather than focusing on establishing concise knowledge of arguments through argumentation or argumentation as in argumentative writing, or focusing on expression and meaning as in narrative writing.

The second characteristic of expository writing is scientific, that is, it must be scientific when introducing, explaining and disseminating knowledge, which can accurately reflect the authenticity and regularity of objective things and does not allow any subjective randomness. Give readers scientific knowledge through accurate definition, proper judgment, reasonable distinction and clear explanation.

The third feature of expository writing is interpretiveness, that is, explanation is the main expression. Compared with the individuality of narration, explanatory language pays attention to universality. Compared with the abstraction of discussion, it pays attention to concreteness. Compared with the sensibility of narration and the logic of argument, it pays attention to clarity.

Description is a language form that specifically and clearly introduces and explains some objective things in a universal sense. Explanatory writing also embodies the purpose of expository writing, that is, through truthful explanation, people can understand physics, give people knowledge and teach people to use it, instead of guiding people to do things through logical reasoning in argumentative writing, unlike narrative writing, which depicts people with emotion to exemplify people.