Is this sentence correct?

[wpqin]

A number of glasses have been prepared and their optical properties examined.

If it's right, why?

[Tdol]

'A number of' takes a plural verb and 'the number of' takes a singular verb.

[wpqin]

'A number of' takes a plural verb and 'the number of' takes a singular verb.

Yes, you are right. However, my question is why the writer used their optical properties examined, did not used their optical properties have been examined . In other words, why did the writer can omit have been.

[RonBee]

Re:

A number of glasses have been prepared and their optical properties examined.

The question regarding this sentence is: "Why isn't have been examined used there?" I'm not sure about that, but I think the correct auxiliary verb there would be were. Thus, the sentence would be: "A number of glasses have been prepared and their optical properties were examined." However, were can be omitted with no loss in meaning. (Perhaps someone else will offer a fuller explanation.)

[Tdol]

A number of glasses have been prepared and their optical properties examined.

If it's right, why?

I'm sorry, I missed your doubt. It would be perfectly correct to repeat the auxiliary verbs, but given that the subject of the two verbs is the same and they are close together in the sentence, there is no need. It simply makes the sentence neater and less repetitious. I'd say it's ellipsis here and 'have been' is left out as unnecessary. If it is included, it is correct, but when there is no need to repeat, we tend to cut out such words:

1 He has finished his work and he has left.
2 He has finished his work and has left.
3 He has finished his work and left.

They all mean much the same, but removing the unnecessary words makes it more concise.

Does that help? :)

[wpqin]

Thank you, teachers.

[Tdol]

You're welcome. :P

[RonBee]

Hm.

It would be perfectly correct to repeat the auxiliary verbs, but given that the subject of the two verbs is the same and they are close together in the sentence, there is no need. It simply makes the sentence neater and less repetitious. I'd say it's ellipsis here and 'have been' is left out as unnecessary. If it is included, it is correct, but when there is no need to repeat, we tend to cut out such words:

1 He has finished his work and he has left.
2 He has finished his work and has left.
3 He has finished his work and left.
They all mean much the same, but removing the unnecessary words makes it more concise.

Very good. You ought to blog that one. :)

8)

[RonBee]

Wondering.

I'm sorry, I missed your doubt.

Is that an example of the teacher picking up something from the student?

(I have noticed several ESL learners say doubt instead of question.)

8)

[wpqin]

You ought to blog that one.

What's that mean?