In the following passage, some words have been deleted. Read the passage carefully and select the most appropriate option to fill in each blank.

Social media companies (1) ______ claim that they promote democracy and are dedicated to the empowerment of ordinary individuals. The assertion (2) ______ entirely unfounded. Recent history shows how (3) ______ citizens have been mobilised against totalitarian regimes on social networking sites. Starting from MeToo to Black Lives Matter, digital networks citizens have been mobilised against totalitarian regimes on social networking sites. Starting from MeToo to Black Lives Matter, digital networks (4) ______ indispensable in bringing together critical voices against social and political (5) ______

Select the most appropriate option to fill in blank number 4.

To determine the most appropriate option to fill in blank number 4, let us analyze the sentence structure and the context of the passage.

The sentence is:
"Starting from MeToo to Black Lives Matter, digital networks (4) ______ indispensable in bringing together critical voices against social and political (5) ______"

First, we identify the subject of the clause, which is "digital networks". This subject is plural.

Second, we analyze the tense and aspect of the sentence. The sentence describes events and trends that started in the recent past (e.g., MeToo and Black Lives Matter movements) and continue to have relevance and impact up to the present day. This requires a tense that links the past to the present, which is the present perfect tense.

Let's evaluate the given options:
- "can": A modal verb that indicates ability or possibility. It does not establish the necessary connection to the ongoing historical context described in the passage.
- "were": The simple past tense. While it is plural, it implies that digital networks are no longer indispensable, which contradicts the ongoing nature of these movements.
- "that": A relative pronoun or conjunction, which does not function as a verb and would make the clause grammatically incomplete.
- "have been": The present perfect tense for a plural subject. This correctly indicates that digital networks became indispensable in the past and continue to be so in the present.

Therefore, the grammatically correct and contextually appropriate phrase to fill in blank 4 is "have been".