BTW, these two CAS built satellites might not be called "M3 & M4" - there's a TV news report after last November's BDS launch interviewing the satellite production facility in Shanghai, and the two satellites about to be shipped back then was marked as "M7 & M8". Perhaps the satellite numbers were issued in blocks.... (come on BDS office, tell us which is which! 
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:drumrolls:
http://tv.cctv.com/2018/01/12/VIDEPenPlOWCqLqxkzy2AeBH180112.shtml 
According to CAS today they have 8 navigation satellites going up this year, so I guess the CAST/CAS satellite distribution will be 10:8 by IOC; an earlier source indicates that CAS will build 10 of the Medium Earth Orbit satellites, making the final distribution 14:10.
The first 6 CAS satellites are apparently given numbers MEO-7 thru 12.
Another social media video of the stage coming down, look out for the orange cloud ...
This is probably why the Chinese need to recover their rockets stages soon....and for reasons other than price: (video of booster falling in planned drop zone from Chinese social media for today's Long March 3B launch, taken at Baise, Guangxi, China)
https://twitter.com/Cosmic_Penguin/status/951654812994514944
Dangerous boosters debris fell from the sky, resulting in a huge explosion
http://weibo.com/2757062934/FDZAzteEQ
EDIT: that original post was deleted
The booster in question was still burning after it impacted the ground. 
China really ought to push forward with booster recovery quicker for this one very reason (should price and "technological advancement" are not enough to persuade them to act quicker). 
Oh I think the Chinese are a bit embarrassed by this kind of stuff, which is why they are gradually A) shifting more launches to Wenchang and B) use kerolox and hydrology with CZ-7 family launchers.
But it takes time... and they aren’t moving any faster than they have to.
This launch used CZ-3B s/n Y45 & YZ-1 s/n Y5.
footage of the booster impact
Note: do no get so close to wreckage like those people, that rocket propellant is Toxic
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