What i the difference between an emission nebula and a reflection nebula

In these nebulae, stars are formed by gaseous material coming together. Ultraviolet radiation emits from the smaller stars and this is the reason why the nebula looks very bright.

Reflection nebulae mostly get the light that they receive from stars that are close by. This is exactly how the moon reflects light from the sun. The nebulae do not have enough stored energy so reflection is the cause of this.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]