Answer: A) adrenaline Explanation: The hormone adrenaline also called epinephrine is known as a stress hormone. In emotional upsets( like fear, anger etc.) this hormone is poured into the blood and it accelerates heart beat. The hormone acetylcholine decelerates heartbeat rate.

Answer: A) TRUE Explanation: Milk is converted into curd or yogurt by the process of fermentation. Milk consists of globular proteins called casein.    It is biochemical change because here microorganism named lactobacillus react with milk and turn it to curd. Lactobacillus required favourable condition to grow. For it 37 degree temperature is needed. But sometimes when it does not get favourable condition, then other microorganism react and makes the curd taste different.

Answer: C) Thunder Explanation: The Sound Following the flash of lighting is because of Thunder.   Lightning is seen earlier than thunder because light travels much faster than sound.   The roar of thunder is the result of a shock wave produced when lightning super-heats the air through which it passes, causing that air to expand very rapidly. This rapid expansion of air creates a shock wave that travels outward at close to the speed of sound.