The play had already been on for quite some time when we _______ at the New Theatre.

—What were you doing when Tony phoned you?—I had just finished my work and________ to take a shower. 

—Would you have come to his help, had you been free? —Yes. But I______ engaged. 

Mr. Lee, who        as a guide for over 10 years, is now a manager in a big travel agency.

The real reason for the fire _______ a burning cigarette end.