Answer:
1. A tall woman dressed in black stood at the door.
2. She will be surprised to hear the news.
3. If unwell, you should not go out to play.
Step-by-step explanation:
A simple sentence is constituted of a singular independent sentence. It has a subject and a predicate, and it is able to convey a full thought on its own.
On the other hand, a complex sentence is constituted of an independent sentence and a dependent one. The dependent sentence cannot stand on its own since it cannot express a full thought.
To transform the sentences in the question into simple sentences, we need to eliminate the dependent clause. One way to do that is to transform it into a phrase without a subject:
"who was dressed in black" --> dressed in black
"when she hears the news" --> to hear the news
"if you are not well" --> if unwell