Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| NGC number | Object type | Constellation | Right ascension ( J2000 ) | Declination ( J2000 ) |
| --- | --- | --- | --- | --- |
| 2129.0 | Open cluster | Gemini | 06h01m06s | °19′20″ |
| 2146.0 | Spiral galaxy | Camelopardalis | 06h18m37.5s | °21′21″ |
| 2158.0 | Open cluster | Gemini | 06h07m25s | °06′ |
| 2168.0 | Open cluster | Gemini | 06h09m | °21′ |
| 2169.0 | Open cluster | Orion | 06h08m32.5s | °57′57″ |
| 2170.0 | Diffuse nebula | Monoceros | 06h07m48s | °23′ |
| 2171.0 | Open cluster | Mensa | 05h58m26.2s | °39′15″ |
| 2172.0 | Open cluster | Dorado | 06h00m05s | °38′ |
| 2173.0 | Globular cluster | Mensa | 05h57m39.7s | °58′41″ |
| 2174.0 | Diffuse nebula | Orion | 06h10m | °30′ |
| 2175.0 | Open cluster | Orion | 06h10m | °30′ |
| 2194.0 | Open cluster | Orion | 06h13m42.4s | °48′06″ |
Question:
Which Object type has an NGC number of 2171?
Answer:
Open cluster