题目内容
关于抑制载波双边带调幅，可以采用的电路不包括
查看答案
搜索结果不匹配？点我反馈
更多问题
关于产生单边带调幅信号的方法，错误的是
Fifteen years ago, most experts would have agreed that the firstpeople in the Americas arrived by walking across a land bridge thatcrossed the Bering Strait between Siberia and Alaska. They thentraveled south through an open area of ground between great sheetsof ice that 1 across North America at thattime. Today, however, this theory is being challengedAn alternative theory suggests that instead of a single first migration,various groups of people came to the Americas at 2spaced well apart in time. Another theory proposes thatancient people might have 3 their way alongthe shoreline using kayaks, just as adventurous tourists do todayLooking at ancient tools found in America, archeologist DennisStanford noticed that their shape was similar to tools used bythe Solutrean culture of southwestern Europe. He thinks it is4 that people of that culture may havekayaked across the Atlantic from Europe to AmericaThe science of archeology often produces theories that are based onvery small bits of evidence. Today's archeologists know that being5 and holding on to one theory while shuttingout the others isn't good science. As new evidence is discovered that6 existing theories, they adjust those theoriesto explain the new facts.
fn. a building or place that provides a particular service or is used for a particular industry
cn. the process of giving careful thought to something
微信支付 
支付宝支付