In "the red-headed league," why does sherlock holmes beat upon the pavement outside of jabez wilson's office?

a.
he wants to find out if the ground under the pavement has been dug out.

b.
he wants to find out where john clay is hiding in saxe-coburg square.

c.
he wants to find out whether wilson can hear him inside the office.

d.
he wants to find out how strong his walking stick is in case he needs to protect himself.

i am thinking its a, but i really dont know, a or b.

The correct answer is:  A.  He wants to find out if the ground under the pavement has been out.   Sherlock Holmes hitting the pavement with his vault was looking for a hollow place, according to the sound emitted by the blow, maybe he is looking for a basement.

the correct answer is the following is a list of inventions made in the medieval islamic world, especially during the "islamic golden age" (8th to 13th centuries),[1][2] as well as the late medieval period, especially in the emirate of granada and the ottoman empire.

science and technology in the islamic world adopted and preserved knowledge and technologies from contemporary and earlier civilizations, including persia, india, china, and greece-roman antiquity, while making a number of improvements and innovations.

answer; incorporation;