Because the have hollow bones, feathers, wings, beaks, and they lay eggs
Uterus<span>Once girls become sexually mature, the outer labia and the mons pubis are covered by pubic hair. A female's internal reproductive organs are the vagina, uterus,fallopian tubes, and ovaries. The vagina is a muscular, hollow tube that extends from the vaginal opening to the <span>uterus</span></span>
<span><span>The blood cells containing hemoglobin, that transports oxygen (O2) to the body tissues of vertebrates, are called red blood cells.</span> Red blood cells (RBCs), are also referred to as red cells, red blood corpuscles, haematids, erythroid cells or erythrocytes<span>, (from Greek erythros for "red" and kytos for "hollow vessel"..RBCs take up oxygen in the lungs and release it into tissues while squeezing through the body's capillaries.</span></span>
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It is B because I had to do this question to
Barometer is used to measure atmospheric pressure :)
