What's the safest place underneath the vehicle to support it on jackstands? Thanks!

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1984 240D Euro 5 Speed 201,000 miles
1984 300D Euro 4 Speed (runs great but ugly)
1984 300TD 185,000 miles
1985 300TD, 240,000 miles
1972 220D, 240,000 miles w/ a stuck odometer
1984 300D, 214,000 miles
1984 300TD, 255,000 miles rustbucket parts car