The three primary germ layers are called ectoderm, mesoderm, and endoderm. once these three layers have formed, the developing trilaminar structure may be called a(

Gastrula

Explanation:

A hollow shaped embryonic structure formed after two weeks of fertilization with three layers is known as gastrula.

The gastrula is formed from the repeated division of the single-layered structured called blastula which later forms three layers called ectoderm, endoderm and mesoderm.

These layers during the process of gastrulation from different organs of the multicellular organisms like the endoderm forms the liver, the ectoderm form the nervous system, the skeletal bone and many others.

Since gastrula structure contains three dermal layers therefore gastrula is the correct answer.

The right answer is B. long distance running.

Sports endurance is what keeps an effort in the long run. Good endurance also makes it possible to find even more pleasure in your favorite sport and makes easier the efforts of the daily life.

In order to become enduring, the athlete gradually increases the distance of your workouts. It does not seem like much but accumulated over time, these small distances will make all the difference. the athlete must also be careful to maintain a slow and steady rhythm.

Many people make the mistake of running too fast during their long session of the week and then have difficulty getting to the end. They have to run slowly and focus on how far they have to go.