Difference between TAKE UP and TAKE ON (= to begin to do something)

Could anyone please give me the answer of the english exercise below and help me tell apart take up and take on, which both mean beginning to do something? I appreciate your help with this exercise.

You looked exhausted. I think you’ve _______ more than you can handle.

A. turned on
B. taken up
C. turned up
D. taken on

Solution 1:

Well. Take up means:

1. to start being keen on smth, to begin doing smth on regular basis.

• I took up tennis.
• I wish I took up mathematics.

And second relevant definition is

2. to consume or occupy.

• The books on finance take up three shelves.
• All my time is taken up with looking after kids.

Whereas take on means

1. to begin to have or exhibit.

• In the dark, the teddy bear took on the appearance of a fearsome monster.

Another definition is
2. to assume responsibility for...

• I'll take on this project if no one else wants to take it.

And I guess, another appropriate meaning of take on is to attempt to fight or compete with.

• I don't recommend taking on that bully, since he is bigger than you.

Therewith, my answer to your question is

You look exhausted. I think you've taken on more than you can handle.

Because it kinda means to assume responsibility for. I guess you see what I mean.