Grey crescent is the area :

The grey crescent is a significant region in the fertilized egg (zygote) of many animals, including amphibians like frogs. It is the area just opposite to the site of sperm entry into the ovum. The grey crescent is important because it is the future dorsal side of the embryo, and its formation is a critical step in the establishment of the embryonic axes (dorsal-ventral, anterior-posterior, and left-right). The correct answer is option (B) just opposite to the site of entry of sperm into ovum. Think of it this way: the grey crescent is a key landmark in early embryonic development, marking the beginning of the dorsal-ventral axis.