So absorbedin the experiment that he didn’t even notice it was already over 12 o’clock.

The stranger to walk into the building in the early morning was probably a salesman.

William found it increasingly difficult to read，for his eyesight was beginning to ________.[ ]

Many Chinese students found______ difficult to learnEnglish grammar.

periment has_________ the possibilityof the existence of any life on that planet, but it does not mean there is nolife on other planets