What is the output of the following command? echo "Hello World" | tr -d aieou

`Hello World` would be the output if no transformation occurred, but `tr -d aieou` specifically removes characters.

`eoo` would only be the output if `tr` was designed to extract vowels, which is not the function of `-d` (delete).

The `tr` command with the `-d` option deletes characters specified in the second argument from the input. Here, `aieou` specifies that all occurrences of lowercase 'a', 'i', 'e', 'o', and 'u' should be removed from 'Hello World', resulting in 'Hll Wrld'.

`eoo Hll Wrld` is a nonsensical combination of deleted and remaining characters, as `tr` processes the entire input stream, not parts of it separately.