．Walking alone in the dark，the boy whistled to ________ his courage.

—When are you leaving for Guangdong?—My plane ________ at six.

— I was surprised to see wild flowers in Alaska. — Many people think there is nothing there _______ ice and snow.

He doesn’t lack ______ to learn. You don’t have to tell or force him to do this or that. 

The total cost of this project will be more than ________ that of the one last century, which is expected to cost below US a score billion.