The correct option to fill in the blanks in the sentence “… Several bad air-crashes recently.” is D. There have been. So, the completed sentence is: “There have been several bad air-crashes recently.”

Here’s why:

• A. There is: This option is incorrect because “is” is used for singular nouns or noun phrases. The word “several” indicates that we are talking about more than one air-crash, so a plural verb is needed.

• B. They are: This option is incorrect because “they” is a pronoun that usually refers to a specific group of people or things that have been mentioned before. In this sentence, we haven’t mentioned any specific group of air-crashes, so “they” doesn’t make sense here.

• C. There were: This option could be correct if we were talking about a specific time in the past. However, the word “recently” indicates a connection with the present, so we need a verb tense that connects the past with the present.

• D. There have been: This is the correct option. The present perfect tense (“have been”) is used to talk about actions or states that started in the past and continue to the present, or actions that have an effect on the present moment. So when we say “There have been several bad air-crashes recently”, we’re saying that these air-crashes happened in the recent past and are relevant to the present moment.

• E. There are: This option is incorrect because “are” is used for actions or states that are happening right now or generally true. The word “recently” indicates that we’re talking about events in the recent past, not the present.