同意曹老师解答观点。

Though much more difficult to understand than the traditional paintings, they were more thought-provoking.

Though （they were 省略了)much more difficult to understand than the traditional paintings, they were more thought-provoking.

在状语从句中，如果主从句主语相同，可以省略从句的主语+谓语

【1】让步状语从句的省略

Though 【he is】a young man, he has made several invention.

He is a good man, though sometimes【he is】rather dull

Even if 【I am】invited to, I will not go to such a bad lecture.

Though 【he was】intelligent, he was very poorly educated

【2】时间状语从句的省略

Work hard when 【you are】young ,or you'll regret.

趁年轻要努力学习，要不然你会后悔的。

When 【she was】young, she began to learn to play the violin.

Mary often helped her classmates when 【she was】free.

Most pregnant women remain off cigarette while【they are】carrying children.

还有其他状语从句省略和前面2种都一样，这里就不全部列出来了。