So difficult ________ it to live in an English-speaking country that I was determined to learn English well．

______ him to do like this, he wouldn’t have made such a serious mistake in his writing.

----- We heard that he had gone abroad.  -----_______.

Helen Keller ever wrote in her article that only through experiences of trial and suffering ______ achieved.

____ by taking part in practice can the young people be toughened and hardened into steel