6) __________ to steel, chromium(铬) increases the metal's hardness.

[A] Added

[B] In addition

[C] Adding

[D] Adds

解析：A为正确答案。(同上)

7) __________ enough food and water, they could have beaten the enemy.

[A] Being given

[B] Given

[C] Give

[D] To give

解析：B为正确答案。(同上)

3. 表示原因

8) Encouraged by his mother, ________________________.

[A] art was studied in Florence by John Singer Sargent

[B] Florence was where John Singer Sargent studied art

[C] the study of art in Florence by John Singer Sargent

[D] John Singer Sargent studied art in Florence.

解析：D为正确答案。四个选项中，只有D的主语为“John Singer Sargent”(人名) ，而只有人才能被“encouraged”(鼓舞)，也就是说，只有D中的主语能充当空白前-ED分词短语的逻辑主语。