He never attempted to ______ any excuse for being late.

A．ionizers don' t have a positive effect on people' s health
B．a feeling of well-being is accounted for only by the presence of' waterfalls or fountains
C．usual animal behavior will predict the coming of a major earthquake
D．whether seismic readings are as effective as watching animal behavior in predicting an earth- quake is not certain

A．Positive and Negative Ions
B．Methods of the Prediction of Earthquakes
C．Ionizer: Best Way to Improve Your Health
D．Fatigue and Headache: Plagues of Positive Ions