Who invented zero?

One of my class 6th students asked, why do we need negative number when in our life we count things from 1,2,3... Can anyone help me in clearing his doubt in an appropriate way? कक्षा छठी के छात्र ने पूछा कि हमे ऋणात्मक संख्याओं(-1,-2,-3...) को सीखना क्यों जरूरी है जबकि हम अपने जीवन में वस्तुओं को गिनने के लिए 1, 2, 3..., यानि धनात्मक संख्याओं का ही प्रयोग करते है? क्या आप मुझे उस छात्र को इसका कुछ अच्छा-सा उतर देने में मदद कर सकते हैं?

Which organ of the body produces the fluid known as bile.

Bchhe ko parivarik rup se pdhai m preshani aaye to teacher kese uski help kr skta h

What is your favorite subject to teach and why?

Which of the following positions was held by Mr. H.J. Kania for the first time in the history of India?