1 . They stood gazing at the happy scene ________ children playing in the park. (用适当的词填空)

2 . Charles Babbage wanted to build a machine that could do calculations ____________ making the mistakes that human “computers” made. (用适当的词填空)

3 . They didn’t know how the thief withdrew money ________ others’ accounts. （用适当的词填空）

4 . The exercises were b________ the abilities of most of the class, so many students failed the test. （根据首字母单词拼写）