In order to keep the balance of ecosystem, every possible means _______to deal with the problems of the over-exploiting of natural resources. 

The US President Obama told the students that he ______ by a single mother who were strict with him and wished him great success in his studies.

---It’s many years since I saw you last time. I _________ you at all. ---I wouldn’t have, either, if someone _________ you by the name.

The theory he had stuck _______ to be true.

 Last year, he wrote to tell me that he ______ his new dance. But I ______ of him ever since.