Is it simple sentence or complex sentence?

[rudiyana]

1. I know what you did last summer.
2. The boy who lives next door is Indonesian.

[lauralie2]

1. I know what you did last summer.
2. The boy who lives next door is Indonesian.

Count the verbs. If there is one verb, then it's a simple sentence.

See also http://www.english-for-students.com/...Sentences.html

[adrimab]

Apart from having two verbs, the sentences also have subordinating conjunctions, in these cases WHO and WHAT. And both clauses (main clause and subordinate clause) can be divided into subject and predicate.

[fatima muhammad shitu]

1. I know what you did last summer.
2. The boy who lives next door is Indonesian.

I know what you did last summer is a simple sentence because it has one subject and one verb. The subject is 'I' and the verb is 'know'.
You can say.. The boy is indonesian( simple sentence). But by adding.. ''who lives next door'' you are just trying to tell your listener more about the boy.So ''who lives next door'' is an adjective clause or adjectival clause.
In a nutshell, all the sentences are simple sentences.