Is "which" optional in this sentence?

In this case, no, you cannot omit which. You are right that which is a relative pronoun modifying that. However, in this sentence, that is functioning as the object of the preposition with:

"...they are reconnected with that..."

If you were to remove that, then the preposition with would not have an object.

Note that this is not to be confused with sentences in which the phrase with which serves as a relative clause. We can say, for example, "The hammer with which I build this table is strong." Here, it is clear what the antecedent of which is: the hammer. But in your sentence, omitting that would give us

"...they are connected with which they have lost..."

which is not the same as the hammer sentence. In this sentence, with which would not be serving as a relative clause because the which has no antecedent. In other words, you need that in order to give an antecedent to which.

No, you need the 'which' as the sentence stands now.

Hi,
I said if I could remove which, not that

Since which functions as the objective in the clause, Can we leave it out?

Ah... my mistake.

Omitting which would still be incorrect, however, because that cannot serve as an object of a preposition and a relative pronoun at the same time. The sentence would still be missing an antecedent noun to which that would refer. As I mentioned in your other thread, what can serve as both because it is essentially a contraction of that which. But by itself, that isn't enough.

Thanks for your quick response.

I still have puzzles.

Could I take the following as the same pattern?

* She followed the calling of that she loved. (I found this one in American Heritage Dict.)

* They are reconnected with that they have lost.

Are you sure you copied it correctly? I'd have to check American Heritage Dictionary, but I found an almost identical sentence on YourDictionary.com, but they put in the correct form. (See Definition 4.)

I copied it correctly.
I want to upload the image, but I don't know how to.

So, how about sentence B now?

I found it. Here is the entry from the The American Heritage Dictionary, the source you said you used:

"1a. Used to refer to the one designated, implied, mentioned, or understood: What kind of soup is that? b. Used to refer to the one, thing, or type specified as follows: The relics found were those of an earlier time. c. Used to refer to the event, action, or time just mentioned: After that, he became a recluse. 2. Used to indicate the farther or less immediate one: That is for sale; this is not. 3. Used to emphasize the idea of a previously expressed word or phrase: He was fed up, and that to a great degree. 4. The one, kind, or thing; something: She followed the calling of that which she loved. 5. those Used to indicate an unspecified number of people: those who refused to join. 6. Used as a relative pronoun to introduce a clause, especially a restrictive clause: the car that has the flat tire. 7a. In, on, by, or with which: each summer that the concerts are performed. b. According to what; insofar as: He never knew her, that I know of."




Thus, Sentence B is still incorrect.

It's a mistake.

I'm terribly sorry


And, Shapeless, Thank you very very much!

It's no problem at all. Glad to be of help.