my macbook pro 13inch does not give me the option to switch from headphones to line in

Which MacBook Pro 13" model do you have?

The older models have a dual port: MacBook Pro (13-inch, Early 2011) - Technical Specifications

Combined headphone/line in (supports digital output)

The newer models only have a headphone port: MacBook Pro (Retina, 13-inch, Early 2013) - Technical Specifications

Headphone port

• Headphone/optical digital audio output (minijack)
• Support for Apple iPhone headset with microphone

If your Mac does not have the the combined headphone/line in port, use an input splitter (for example this 2x 3-Pin 3.5mm Headset Splitter Adapter - M/F http://www.amazon.com/dp/B004SP0WAQ) or an audio interface; the most basic would be the iMic Recording with iMic in GarageBand

And have you tried to set the input up as described here?

MacBook and MacBook Pro (13-inch): How to use the combination audio port for an audio input device

The device needs to be plugged in with a mini-stereo plug and to be turned on, otherwise the mac will not recognise the port as an input port.