Combine the two sentences using either a coordinating or subordinating conjuction.
He was surprised. He didn't expect it.
He was surprised because he didn't expect it.
Complete the following task based on the instruction and optional input provided.### Instruction:
Combine the two sentences using either a coordinating or subordinating conjuction.

### Input:
He was surprised. He didn't expect it.

### Output:
He was surprised because he didn't expect it.