Through experiments,the writer found that preparation in advance can help examinees improve complication,accuracy and fluency in grammar,while instant preparation can help examinees improve accuracy of oral expression and complication in grammar.

This paper is concerned with single machine stochastic scheduling problems with random ready times, processing times and due dates to minimize the number of tardy jobs.

In this paper,we consider a semi on-line scheduling problem on two uniform machines with machine available times,where the objective is to minimize makespan of the schedule.

In the first case, if the machines are uniform ones with available time, we assume that the total processing time is known in advance.

In the paper,we consider a semi-on-line scheduling problem on two uniform machine system(different machine speed) with different machine available time,to reach the purpose optimizing availability,where the objective is to minimize makespan of the schedule.