Origins of the Domino Theory. In September 1945, the Vietnamese nationalist leader Ho Chi Minh proclaimed Vietnamâs independence from France, beginning a war that pitted Hoâs communist-led Viet Minh regime in Hanoi (North Vietnam) against a French-backed regime in Saigon (South Vietnam).
The human range is commonly given as 20 to 20,000 Hz, though there is considerable variation between individuals, especially at high frequencies, and a gradual loss of sensitivity to higher frequencies with age is considered normal.
Frequency is measured in Hertz (Hz). A person with hearing within the normal range with respect to pitch of sound can hear sounds that have frequencies between 20 Hz and 20,000 Hz. The most important sounds we hear every day in the speech of others are in the 250 to 6,000 Hz range.