1. a. Dependent claims 3 and 4 do not cite any of the preceding claims. This means: claims 3 and 4 do not cite any of the preceding claims. I think you Claims 3 and 4 must be written in the form of "according to claims 1 and 2..."~~
b. Your understanding is correct, it should be written as "1 or 2" That’s it
2. c. Theoretically, the replacement of the modified document can be all or part of the replacement. For example: claims 3-4 are modified and other claims are not modified at all, and they are all in the rights. On page 1 of the claim, you can submit only page 1 of the newly revised claim to replace the original page 1. However, from the perspective of convenience for the examiner, it is better to replace all the claims and submit a new claim. The document replaces all the original claims; which part is modified shall be submitted. For example, if you only modify the claims, you only need to submit the replacement documents of the claims~
"Replacement of Amended Application Documents" "Document" essentially refers to a revised application document unit such as the newly submitted claims or description or description drawings
d. Replacement document in revised format "refers to providing a revised comparison The purpose of this page is to allow the examiner to quickly understand the specific content of the applicant's modifications, such as which claims are involved and what type of modifications are made. For example, when the document is revised using Word, there will be marks on it, not all of them. After accepting the revision, what remains is the document with traces of modifications; or you can clearly describe where and what kind of modifications have been made in the opinion statement of the supplementary document ~ as long as the examiner can know the specific content of the modification in any way ~Usually a document marked with common symbols such as deletion, addition, replacement, etc. on the original document~