You should be careful in the sun.

在阳光下你要当心。

A: How are you feeling now?

A: 你现在感觉怎么样？

B: Much better, thanks.  It's good to go out.

B: 好多了，谢谢。出去走走一定很好。

A: Good. But you should put something on your head. Have you got a hat, or some sun screen?

A: 好。但是你头上应该戴些东西。你有帽子或者防晒霜吗？

B: Why?

B: 干嘛？

A: It's very hot and sunny today. You should be careful in the sun. You might get sunburnt¹.

A: 今天非常热，阳光强。在阳光下要当心。你可能会被晒伤的。

B: You worry too much! I'll be OK.

B: 你担心得太多了。我会没事的。

1. Many people don't realise² how careful / careful you have to be in hot sun. You can try to persuade them -! You should be careful in the sun. / You should be careful in the sun.
很多人没有意识到在炎热的阳光下应该careful /当心。你可以这样劝说他们You should be careful in the sun. /在阳光下你要当心。

2. You can give advice about wearing a hat / a hat or using sun screen / sun screen: You should put something on your head. / You should put something on your head. / Have you got a hat? / Have you got a hat? / Or some sun screen? / Or some sun screen?
你可以提出戴帽子/ a hat或者用防晒霜/ sun screen: You should put something on your head. /你头上应该戴些东西。Have you got a hat? /你有帽子吗？Or some sun screen? /或者有防晒霜吗？