先学习black有助于学习blackboard，属于（ ） 。 

(单选题)42. （ ） (单选题)41.（ ） (单选题)40.（ ） (单选题)39. （ ） (单选题)38.（ ） (单选题)37. （ ） (单选题)______ I arrived earlier, I could have caught that bus. (单选题)If we ______ hard in the past few years, things ______ to sm (单选题)Hardly ______ when a student came to visit her. (单选题)My mother thought I can’t take care of myself, so she didn’t