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The skeletons of chickens are adapted to support flight and fast movement. Although chickens are flightless birds, their body manages to have a rather high jump. Their beaks, made up of keratin, are much lighter than a bony jaw.

The fluid sacs that protect the embryo are called the extraembryonic membrane. Chickens are vertebrates that lay their eggs outside on the land, These eggs need to protect their embryo; thus, the extraembryonic membrane is adapted.

Thus, the extraembryonic membrane is the structural adaptation that helps chickens lay their eggs in an arid environment rather than water.

Therefore, the given option is correct.

The presence of a yolk sac is critical for the development of the embryo. The yolk feeds the embryo and facilitates the exchange of gases between itself and the mother. It also serves as a location for the manufacture of blood.

Thus, the yolk is not an important structural adaption for the chicken embryo.

Therefore, the given option is incorrect.

Cleavage is a critical process for embryonic development. Cleavage leads to the development of a multicellular embryo. Due to cleavage, the embryo possesses different developmental regions.

Thus, cleavage is not a structural adaptation for the chicken embryo.

Therefore, the given option is incorrect.

Gastrulation is the process of differentiating the embryo structures. The blastopore develops into three germ layers, endoderm, mesoderm, and ectoderm; this process is called gastrulation.

Thus, gastrulation is not a structural adaptation for the chicken embryo.

Therefore, the given option is correct.