______ a certain doubt among the people as to the practical value of the project.
Scientists are still wondering ________ the Egyptians built the pyramids so long ago.
________ about the man wearing sunglasses during night that he was determined to follow him.
I am certain by no means ________ his word since he has promised an amount of money to the poor.
It is comforting to see that ________, we are doing our part for the environment.
We are thinking about ________ can be admitted into our club. The number of members is limited.