Final answer:
An infant is expected to hold its head up while in the prone position at two months of age. Crawling on the floor and creeping on the floor happen at later stages of development.
Step-by-step explanation:
By the age of two months, an infant is expected to hold its head up while in the prone position. Crawling on the floor typically occurs around ten months of age, while creeping on the floor usually happens by the age of six months. Sitting up steadily without support is a milestone that typically occurs by the age of twelve months.