Which of the Following Trigger Mechanisms for the Initiation of Stellar

Which of the following trigger mechanisms for the initiation of stellar formation in gas and dust clouds produces many high-mass O and B stars but only a few low-mass stars?

A) passage of the cloud through a black hole
B) compression caused by the passage of the cloud through a galactic spiral arm
C) shock waves from a supernova explosion
D) gravitational condensation of the cloud