<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def render_template(process, template_string, context):
 """Render template using the specified expression engine."""

    from resolwe.flow.managers import manager

    # Get the appropriate expression engine. If none is defined, do not evaluate
    # any expressions.
    expression_engine = process.requirements.get('expression-engine', None)
    if not expression_engine:
        return template_string

    return manager.get_expression_engine(expression_engine).evaluate_block(template_string, context)