When            to someone,I usually say, "Pleased to meet you."

introduce

introduced

introducing

am introduced

考查过去分词和省略。句意：当我被介绍给别人时，我通常会说：“很高兴认识你”。根据句子结构可知，本句是when引导的时间状语从句，原句when I am introduced to someone,这里当从句主语与主句主语一致时，并且从句的谓语动词有be这时从句的主语与be同时省略，所以空格处introduced。故选B项。

What some people regard as a         is seen as a plus by many others.

duty

drawback

failure

faith

考查名词词义辨析。句意：一些人认为是一个缺点，而其他许多人则认为这是一个优点。A.duty责任；B.drawback缺点； C. failure 失败；D. faith信念。根据空后plus“优点”可知，空处需用drawback“缺点”与之对应。故选B项。

Let's learn to use the problem we are facing         a stepping-stone to future success.

to

for

as

by

考查介词词义辨析。句意：让我们学会把我们所面对的问题作为通向未来成功的手段来利用。A.to朝，对 ；B.for 为了，对于；C.as 作为；D.by通过，凭借。根据句意可知，此处“作为”符合语境。故选C项。

--What is happening in that new area?

---New houses          over there.

are built

are building

have built

are being built

考查时态和语态。句意：在那个新区域里发生什么事情了？那儿建起来许多新的大楼。根据第一句时态is happening 可知，时态用现在进行时，故第二句也要用现在进行时，主语 houses与build 建立之间是被动关系，故用现在进行时的被动语态（am/is/are being done），此处为are being built，故选D项。

It has been warned that        to the surroundings with people infected by Covid-19 without any

protection can lead to severe result.

being exposed

exposed

having exposed

to expose

考查非谓语动词。句意：有人警告称，在没有任何保护措施的情况下，暴露在有感染 Covid-19的人环境中会导致严重的结果。分析句子结构可知expose在句中应用非谓语动词形式，表示“暴露”短语为be exposed to,且从句中缺少主语，expose 与主语people是被动关系，故应用动名词的被动式作主语。故选A项。