The correct option is
A Bat has a milk secreting gland
Bat is placed in class Mammalia because they give birth to a live young one who survives by sucking milk from mammary glands through nipples. The mammary glands are the exocrine gland which produces milk to nourish neonate and they are found only in class Mammalia of the entire animal kingdom.
The taxonomic classification of the bat is:
Kingdom: Animalia
Phylum: Chordata
Sub-phylum: Vertebrata
Class: Mammalia
Order: Chiroptera
So, the correct answer is 'Bat has a milk-secreting gland'.