The great migration on the u.s. home front during world war 1 involved

b. African Americans moving north from the South to work in factories.  

Explanation:

Apparently aimed at visiting American comedian Bob Hope, a time bomb set by Viet Cong terrorists exploded at Brinks, a U.S. Army officers club in Saigon, killing two Americans and wounding 50 others.Three years later, a captured memorandum was located that had criticized the terrorists for the fact that "The bomb exploded 10 minutes before the set time. Shortly after the explosion the cars of the Bob Hope entertainment group arrived. If the bomb exploded at the scheduled time, it might have killed an additional number of guests who came to see the entertainment."

Hope was making his first Christmas visit to South Vietnam, and he and his 60-member troupe entertained 1,200 servicemen at the Bien Hoa Air Base. He opened by joking, "Hello, advisers. Here I am in Bien Hoa... which is Vietnamese for 'Duck!!'". Referring to his surroundings as "Sniper Valley", he said, "As I flew in today, they gave us a 21-gun salute... Three of them were ours."

Unemployed electronics engineer Tom Osborne completed the prototype of the first desktop electronic calculator after more than a year of work at his home workshop, then spent another six months trying to find a buyer for his "Green Machine" (so called because he constructed the prototype casing from balsa wood painted green). After more than 30 rejections, he was able to sell the invention to the Hewlett-Packard company in Palo Alto, California.