B: The preposition "V-ing" sentence pattern of the present participle structure ..., the main sentence ... "indicates the reason.
C: The sentence pattern before the adjective phrase "adj" and the main sentence "..." indicate concession.
D: there is a time difference with B.
So, choose B.
Look at the original text and translation:
Fully aware of the importance of his invention, Bell wrote to his father and said, "One day, telegraph lines will be installed at home like water or gas, and friends can talk to each other without leaving home. The patent was granted in 1876, but it was not until five days later that Bell sent the first telephone message to his assistant Watson. This sentence has become famous now: "Mr. Watson-come here-I want to see you." Alexander Graham Bell is not a man who has a good rest. He is interested in many other fields of invention. He experimented with helicopter design and aircraft. While looking for a kite that could carry a man into space, Bell tried to put triangles together and found the shape of a tetrahedron. Because it is very stable, it has proved to be very valuable in bridge design. Bell was an inventor all his life. He invented the first invention at the age of 1 1 and completed the last invention at the age of 75. Although he is most often associated with the invention of the telephone, he is indeed a person who constantly seeks practical solutions to improve everyone's quality of life.
Fully aware of the importance of his invention, Bell wrote to his father: "This day is coming, just like water and gas, every household will lay telegraph lines, and friends can chat and talk without leaving home." 1876, this invention was patented, but only five days later, Bell sent his first telephone message to his assistant Watson. This sentence is now a household name: "Mr. Watson, come here, I want to see you." Alexander Graham Bell did not do it once and for all. He took an active part in inventions in many other fields. He has tried helicopter design and airplanes. In order to invent a kite that can carry people in the air, Bell tried to tie many triangles together and then found the shape of a tetrahedron. Facts have proved that tetrahedron has inestimable value in bridge design because it is very stable. From the first invention of 1 1 to the last invention at the age of 75, Bell has been inventing all his life. Although people will think of the invention of the telephone when they think of him, in fact, he has been exploring and seeking practical solutions that can improve everyone's quality of life.