Even though I have not read this I am going to guess that it is A.
Answer:
This coming Friday is May 1. In normal times that day offers numerous reasons to celebrate, but the need for social distancing will make it less enjoyable this spring.
Food, gas and clothing were rationed. Communities conducted scrap metal drives. To help build the armaments necessary to win the war, women found employment as electricians, welders and riveters in defense plants. Japanese Americans had their rights as citizens stripped from them.
The main way in which the Huang He River contributed to the growth of the Chinese civilization was that it provided crucial irrigation to the surrounding fields, which greatly increased crop growth and cultivation.
Hi!
The answer is 3. All these answers are correct.
Practical radio communication was furthered by enthusiasts who were experimenting with Hertz and Maxwell's findings.
By the theory of modulation because it helped establish the earliest method to transmit voice by radio.
By the use of vacuum tubes because they made detection and amplification of radio signals possible.
So, all of these 3 factors furthered the development of practical radio communication.