Rain is what only comes down but never goes up.

Answer: A) Tooth Enamel Explanation: Tooth Enamel is the hardest and most highly mineralized substance in the human body. It is a tissue and not a bone. This tissue has high mineral content which makes it hardest substance.   Femur and Temporal bone of the skull are the hardest bones of the human body.

Answer: A) Hydrogen sulphide Explanation:

Answer: B) 50 Explanation: Sony and her brother's age sum is 31Let Sony's mother's age be 'x'.Now the conditions given for both of their ages related to their mom is1/5(x-15) + 3/5(x-10) = 31x-15 + 3x-30 = 1554x-45 = 1554x = 200x = 50So, Mother's age = 50. Cross verification : 15 years ago age = 35 => Sony age = 710 years ago age = 40 => bro age = 24 Sum = 24 + 7 = 31.

Answer: A) 330/29 m/s Explanation: Second gun shot take 30 sec to reach rahul imples distance between two. given speed of sound = 330 m/s Now, distance = 330 m/s x 30 sec    Hence, speed of the bus = d/t = 330x30/(14x60 + 30) = 330/29 m/s.

Answer: A) 6CO2 + 6H2O -----> C6H12O6 + 6O2 Explanation: Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms activities.   Photosynthesis can be represented using a chemical equation.   The overall balanced equation is                 6CO2 +  6H2O   →Sunlight    C6H12O6   +   6O2Source of Carbon & Oxygen  + Source of Electrons & Hydrogen + Energy that drives Photosynthesis             ----> Sugar + Gas produced by splitting water.   Where  CO2 = carbon dioxide  H2O = waterC6H12O6 = glucose  O2 = oxygen.

Answer: A) Pila globosa - pearl Explanation: Pinctada vulgaris is a bivalve from which pearl is obtained.

Answer: A) if a > b Explanation: I.  (a - 3)(a - 4) = 0   => a = 3, 4   II.   (b - 2)(b - 1) = 0   => b = 1, 2   => a > b