71.   Billings has staked his reputation on making his designs worry-free, and knows his stuff.

72.   Billings knows his stuff.

73.   He knows his stuff.

74.   The older a teacher is, the more effective they become because they know their stuff well.

75.   They say she knows her stuff but worry about her priorities.

76.   When it comes to talking crime, South Africans know their stuff.

77.   The elder Floyd must know his stuff.