a. The rector at any time;

b. The wardens, if there is no rector, or if the rector is absent from the diocese for three calendar months, or is incapable of acting, or if the rector has refused to call the meeting within one week after the receipt of a request signed by a majority of the members of the vestry; or

c. A majority of the members of the vestry, in case of failure of the wardens to call such meeting within one week after the receipt of such request.