Generally, an ultrasound is performed for all women at this point. the fetus can suck its thumb, yawn, stretch, and make faces.

By the fourth month of pregnancy the heartbeat of the baby can be audible with the help of Doppler ultrasound. It can also evaluate the flow of blood through the arteries and veins to various organs of the body.

By the fourth month of pregnancy the baby's toes and fingers are in well defined stage. Formation of eyebrows, eyelids, nails, hair and eyelashes occurs. The bones and teeth increase density and by this time the baby is able to suck his or her thumb, make faces, stretch and yawn. The genitalia and the reproductive organs get fully developed and this can be detected using the ultrasound technique.

In the ultrasound technique very high frequency sound waves are passed through the lower abdomen by the probe or transducer. /this transducer then collects the sounds which bounce back and these sound waves are then used to produce an image on the computer screen attached.

it creates acid rain

answer: ice crystals in air

the water from the water body or another source of water gets evaporated as water vapor as an effect of heat on water. these water vapor rises in the upper layers of the earth atmosphere under high atmospheric pressure. the atmospheric pressure of these water molecules starts to decrease due to the effect of cold air. the invisible water vapor condenses into visible water droplets and ice crystals.these ice crystals and water droplets being less denser than the surrounding air floats on air as clouds.