Explanation:

Correct Answer is (b).The original sentence is incorrect.
Reason: There are two errors in the bold part.
Firstly, the term ‘tension trade’ is absurd. Here, the writer makes a reference to trade war. A trade war happens when one country retaliates against another by raising import tariffs or placing other restrictions on the opposing country's imports. Therefore, ‘tension trade’ must be replaced by ‘trade tension’ in order to make the sentence correct.
Secondly, the author means to convey that trade tension has heightened. Therefore, “heightened due to” should be replaced by “due to heightened” to make it a grammatically correct sentence.
Among the choices available, option B replaces the bold part most appropriately.The sentence after replacement becomes:
Due to heightened trade tension, which has been putting pressure on global growth, gold has been witnessing safe haven buying.Option B is hence the correct answer.