Which of these is a property of acids?
a. they produce hydrogen gas when reacted with metals
b. they taste bitter
c. they feel slippery
d. they turn litmus paper blue

The correct answer is
A. Hydrogen gas when reacted with metals.
(Also I took the quiz and this was the correct answer so I hope this makes you feel more confident with your answer!) 

The  grandmother cell  is a hypothetical  neuronthat represents a complex but specific concept or object.[1]  it activates when a person "sees, hears, or otherwise sensibly discriminates"[2]  a specific entity, such as his or her grandmother. the term was in use at least as early as 1966 amongst staff and students in the department of experimental psychology, university of cambridge, england. a similar concept, that of the  gnostic neuron, was proposed two years later