With the help of high technology, many new substances（物质）______in the past years.
#102927
A
discovered
B
have discovered
C
had been discovered
D
have been discovered
推荐题目
Visitors ________ not to touch the exhibits.
#99747
A
will request
B
are requested
C
are requesting
D
request
Fei Junlong’s wife and his child ________ to see him off before the launch, but they failed because of the rules.
#104310
A
hope
B
had hoped
C
have hoped
D
were hope
They _______ on the program for almost one week before I joined them, and now we ________ it as no good results have come out so far.
#104610
A
had been working; are still working
B
had worked; were still working
C
have been working; have worked
D
have worked; are still working
The train ＿＿＿＿＿ at the present speed until it reaches the foot of the mountain at about nine o’clock tonight.
#104661
A
went
B
is going
C
goes
D
will be going
I first met John at my sister’s wedding. He _________ with the bridegroom at the time.
#100052
A
was talking
B
talked
C
had talked
D
had been talking