在双缝干涉实验中，屏幕上P处是暗条纹，则两束相干光在P处的光程差可能是（）

Goodparentshavetheabilitytocommunicatemessagesoflove,trust,andself-worth______theirchildren

Onehundredmiles____(be)toofartotravelonfoot.

MaryacceptedDavids___(invite)tojoinhimforlunch.

Hetookhisumbrellawithhimlestit____(rain).