渗透探伤主要用来探测（）。
参考答案：非铁磁性材料的表面和近表面的焊接缺陷
请看图将下列句子补充完整，注意冠词的使用。
1. What's this? It's ________________.
2. What's this? It's ________________.
3. What's that? It's ________________.
4. What's that? It's ________________.
5. What's that? It's ________________.
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