This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Growth, Development, and Behavior, Subject name: Pediatrics
By what age is the milestone of climbing steps with alternate feet achieved? 
Select and explain. 
A. 2 years, B. 3 years, C. 4 years, D. 5 years
B: 3 years
Answer: B: 3 years 
Explanation: Ans. is 'b' i.e., 3 years Gross motor development milestonesNeck holding3 monthsSitting with support5 monthsProne to supine and supine to prone6 monthsSitting without support8 monthsCrawling9 monthsCreeping10 monthsWalking with support11 monthsWalk independently1 yearRun well, climbing upstairs and going downstairs with one step at a time2 yearsRide tricycle; climbing upstairs with alternate feet3 yearsHopping; going downstairs with alternate feet4 yearsSkipping5 years