Question 37: I had met her three times before. I didn't recognize her. (Although)
=> Although  I had met her three times before, I didn't recognize her
Question 38: Nam must chew food carefully. Otherwise, he will have a stomachache. (If)
=> If Nam chews food carefully , he won't have a stomachache
Question 39: My teacher spoke very fast. We can't understand what he was speaking. (too)
=> My teacher spoke too fast for us to  understand what he was speaking
Question 40: Son Doong Cave is recognised as the largest cave in the world. It is located in Quang Binh Province. (which)
=>Son Doong Cave , which is located in Quang Binh Province ,  is recognised as the largest cave in the world
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