Explanation:

The Prime Minister was ______ a ceremonial welcome.

To find the correct answer for the blank we need to check the meaning of the words given as options.

1. expected - regarded as likely; anticipated

2. invited -  make a polite, formal, or friendly request to (someone) to go somewhere or to do something.

3. initiated  - cause (a process or action) to begin.

4. extended - lasting longer than is usual or expected; prolonged..

Hence option 4 is the most suitable answer for filling in the blank.