Step 1: Evaluating each sentence.
- (A) "I have returned all the books to the library yesterday" is incorrect because the present perfect tense ("have returned") does not fit with a specific time in the past ("yesterday"). The past simple tense should be used instead: "I returned all the books to the library yesterday."
- (B) "Though Ram worked very hardly, he failed" is incorrect because "worked hardly" is grammatically wrong. The correct form is "worked very hard."
- (C) "Everyone admired his courage" is correct. This is a grammatically sound and meaningful sentence.
- (D) "I should like to travel in the abroad" is incorrect because "in the abroad" is not a standard phrase. The correct phrase is "abroad" without "in."
Step 2: Conclusion.
The correct sentence is "Everyone admired his courage."
Final Answer: Everyone admired his courage.