Does ProxyChains use all proxies in dynamic_chain or just one?

Let's say, I have dynamic_chain set and have two proxies in the chain list:

[ProxyList]
socks4  127.0.0.1 9999
socks4  127.0.0.1 8888

Both proxies can reach the server aa.bb.cc.dd. When I run the following command:

proxychains ssh aa.bb.cc.dd

How will be the route to reach aa.bb.cc.dd? Will it pass by 127.0.0.1:9999 and then by 127.0.0.1:8888 and finally to aa.bb.cc.dd? Or it will go directly from 127.0.0.1:9999 to aa.bb.cc.dd? Or it will go directly from 127.0.0.1:8888 to aa.bb.cc.dd? I am much confused about this. Can any friend show me what the actual case it is? Many thanks!